The following examples are games organized by genre and arranged in order of most linear gameplay to least linear gameplay. The linear games will be easy enough to describe. I will describe the more emergent games in terms of gameplay design feature(s) that make them emergent (dynamics, depth, alternate paths, etc). The videos show examples of gameplay of the games. Click the "next" button to advance to the next example in the playlist.
Rhythm Heaven -> Guitar Hero -> Rock Band Blitz -> Wii Music. The rhythm-action genre of video game is one of the most linear genres. Since most of these games are designed around syncing player inputs with recorded music tracks, there tends to be little deviation from the linear score. In other words, rhythm-action gameplay tends to be linear because the music is linear. In general, players must act on the beats to win or else miss beats and eventually fail.
Rhythm Heaven is about a simple as it gets for a rhythm-action game. Using the touch screen as a huge button, players tap, release, flick, and scratch to the beat. That's it. No alternate tracks. No layered music. Just a simple challenge to hit the right beats when promted by visual and auditory cues. Each level presents the same sequence every time you play. Dance Dance Revolution, Elite Beat Agents, Guitar Freaks, Osu! Tatake! Ouendan!, and Jam With The Band are all games that are as linear as Rhythm Heaven.
Guitar Hero would belong in the same category as Rhythm Heaven if it weren't for the star power that can be activated at different times and the occasional section where players can jam in lots of notes to earn more points. Because the goal of Guitar Hero is to survive to the end while earning as many points as possible, activating star power is a player mechanic that puts the game into a different state that's relevant for goal-seeking. Players can activate star power whenever they want to earn more points from correctly played notes or to save themselves from failure. Furthermore, using the whammy on long star notes to increase the amount of star meter you gain is an valid option that adds to the emergent potential of the game, though by a small amount. DJ Hero lets player use their star power and rewind the track back in different places allowing for more emergent control over the sequence of the music and challenge.
Rock Band Blitz and games like Frequency give players multiple tacks of music to move back and forth between. Though the song progresses forward in a linear fashion like other rhythm-action games, switching tracks let's players alter the sequence of rhythm based challenges to a large degree. If you don't like the challenge on one track, just switch over. With up to 5 tracks to switch between the non-linear gameplay is clear.
Wii Music has one major emergent feature that puts it at the top of this list; improvisation. At any time during the linear music track players can play notes in between the suggested notation. Players are free to swing the rhythm, hold notes, add flare, and really express themselves in a musical way. The only problem I have with putting this game on the list is that the "goal" may not be very clear. Though you may be graded on how well you play the notes, the game doesn't grade you on how well you improvise (if such a thing can be graded). So if your goal is to make music, which seems to be the goal of the game, then improvisation counts as a significant element of emergent potential. If your goal is to play the right notes as notated, then being able to improvise does not count.
Super PSTW Adventure RPG 2009-> Linear RPG -> Find Mii -> Final Fantasy 13 (before Gran Pulse) -> Radiant Historia -> Pokemon Black/White. RPG adventures typically set players on a path of a hero who fights through one obstacle after another until saving the day. RPG leveling systems allow players to gain experience and grow stronger by overcoming challenges of high or low difficulty. Though such a design gives players the emergent freedom to approach challenges at different levels, we still have to look at the sequence of actions necessary to overcome these challenges.
All you can do in Super PSTW Adventure RPG 2009 is press the spacebar to win, hence the title. There is only one place you can actually fail in the game, and it's a QTE. The game is a parody of epic RPG adventures highlighting the fact that some RPGs seem to offer lots of meaningful choices when you're essentially locked into a linear progression of events. Regardless of your thoughts on this subject, Super PSTW is as linear as "RPGs" get, which is funny considering the next example.
Linear RPG is another a parody of RPGs. With random battles, HP, EXP, and a story Linear RPG is very much a video game. Though it seems like all you do is hold forward and grind to progress, you still have some control over when, where, and how long you grind. Some may call into question the meaningfulness of the choices you can make. An important point to realize is that even if the choices are seemingly meaningless, Linear RPG is non-linear as long as there are at least 2 sequences of choices to make to obtain victory. In this case, there's a random element to the invisible random battles that defines the basic risk-reward balance of player choices. This means you can grind and be safe, or you can take your chances and hope to survive until the next checkpoint. This choice isn't meaningless, it's just simple because the game is simple. Yes, the campaign is linear (there are no side quests). Yes, the story is linear too. But the gameplay is not linear (just barely). This is easier to understand when you compare your experience with Linear RPG to Super PSTW.
Find Mii challenges players to conquer the Mirage Tower to save the king. There's only one path to take making the campaign linear. The gameplay, however, is non-linear in that players have many viable strategic options. Players can hire random (low level) warriors, street pass and level up from other 3DS users, cycle through which teammate will attack next, and chose between physical attacks (which can miss) or from various magic spells with effects that vary with the Mii's shirt color. Some players have chosen to brute force their way through by hiring tons of low level warriors. Others, like me, leveled up with close family and friends and used the low level warriors to fill out the rest of the team. Some use physical attacks and roll the dice. Others rely on the security of magic attacks. Though some enemies are hard counters forcing players to execute a particular counter strategy, for the most part there are many options to explore that are all capable of victory.
Final Fantasy 13 before Grand Pulse is a lot like Find Mii in that the campaign or macro level progression is very linear while the micro level, moment-to-moment combat is gives players options. Compared to other RPGs and other Final Fantasy games, many gamers feel that FF13 campaign is very linear before it opens up half way through the compaign at a location called Grand Pulse. Whether or not FF13's campaign progression is actually more linear than other FF games is hard to say. Certainly towns, overworld maps, and talking to NPCs are great interactive elements that can make any linear campaign progression less obvious by breaking up the pacing. Because the first 10-20 hours of FF13 lacks many of these interactive elements, I can see why the game at least seems more linear. Aside from the paths looking like corridors with obvious side pockets to collect obvious loot, there is little you can do to vary the sequence of the campaign progression in the begining of FF13.
Zooming into the micro level we should look to FF13's battling. From a game design perspective, we look at various mechanics and player options in terms of a game's design space and interplay design. These two types of analysis help us identify design waste, unique choices, and functionally useful options. Though I didn't dive into the FF13 systems very much, I can easily say that the combat is non-linear. The paradigm shift system gives the player options to try different strategies.
I know that FF13 has far more complexities than Find Mii does, but I wonder if it's deeper. After all, there are games like Knights in the Nightmare that are filled with complexities, systems, and details that ultimately fall flat depth-wise (interplay). In general, it seems that RPG battle complexities and systems naturally create options that make the micro level gameplay increasingly non-linear. The next example features a very non-linear macro level campaign.
Radiant Historia is an RPG with time travels as a central theme and mechanic. As players progress they have the freedom to travel to any previous event in time and replay them to alter history. Like Zelda: Majora's Mask, the details in the environment and the NPCs are important puzzles and side quests in themselves. On the macro level the side quests, alternate histories to explore, and the multiple endings makes the campaign very non-linear. On the micro level Radiant Historia features non-linear gameplay through battle options of customizing items, weapons, and characters. The battle system has depth utilizing a spatial grid enemy layout.
Pokemon Black/White is a very non-linear game with a fairly linear looking, classic-JPRG presentation. On the micro level players have the common RPG trappings to work with and customize to pursue the goal. Take your pick from among 150 different Pokemon to build your team. Customize them with hundreds of attacks, hold items, and other attributes. The turn-based combat is deep enough for competitive play which gives the game enough significant variation and enough interesting choices to make countless of possible ways to win.
On a macro level Pokemon has many secrets, side quests, and other diversions to alter the sequence of the campaign progression. From fighting on battle subways, becoming a research aid, trading, breeding, and more there's a lot to do in Pokemon outside of the main quest. New features to Black/Whate are at any time players can invade each other's game worlds via local wireless connections or transfer Pokemon into the online Dream World. The point is, you have lots of options to explore in the game and they only expand once you beat the game. Whether the actual stories branch and diverse like in Radiant Historia, or the story remains the same and players merely explore the world in a number of different orders like in Pokemon, these RPGs are non-linear on the micro and macro levels.
Cursor 10 -> Plants vs Zombies -> Starship Defense -> Star Craft 2. Real-time strategy games generally feature units or resources of some kind that players use to work toward a goal while time and some kind of decay element provides the core dynamic of the challenge. The design difficulty for most RTSs comes from creating a gameplay system of interesting choices. If there was just one winning strategy, these games wouldn't work as well. So we're inherently dealing with non-linear games for this genre.
In Cursor*10, a self-cooperative game where players must progress from floor 1 to 16 through a linear series of stairs. In fact, there's only one randomized element in the entire game and that's on floor 4 where the stairs are hidden under a random box. Though not based on combat, this game is a simple real-time action game where one can apply a notable amount of strategy. With your 10 cursors there are many different roles you can execute like pushing ahead, holding doors open, or clicking cones for extra points. Whether you go for a high score or just go for the win, the exact sequence of actions you take is non-linear while the overall progression is linear.
Plants vs Zombies is a tower-defense game with more complexities than Cursor*10. Though the difficulty curve may be very smooth creating an easy experience for some gamers there are still different sequences of actions players can take to win. Even before players get enough plants to create custom decks, players can place plants in different places at different times. Like with the RPG example, more complexities generally means more choice and more emergent possibilities.
Strategy in games is all about specific plans of actions for gaining some kind of advantage. The specificity involves knowing the rules on a very detailed and even nuanced level. Typically the more you know the better strategies you can use. So, in many ways the difficulty of a challenge is an important consideration in our analysis. There's a balance to strike between interesting choices and strategy. You can't let players do anything they want and win because this would undermine the knowledge skills required of strategy. And you can't have just one viable solution because that level of limited options and strict linearity would defeat the purpose by reducing the gameplay to a solution rather than a system of interconnected dynamic rules and conditions. Can see why the balance is tricky? When systems are designed with more interplay and dynamics as they grow in complexity, this balance is easier to maintain.
Starship Defense strikes a balance well. To earn a medal on each level, players have to understand the battle conditions and execute on a few viable strategies with little room for error. While the gameplay gives players options for which weapons to use, where the place them, and when, going for the more difficult goals challenges player to find the relatively few possibilities to achieve the best possible results. Such is optimization. On a micro level it's the options players have and the variety of sequence possible that make Starship Defense non-linear. On a macro level, the campaign has branching paths and optional challenges that add variety to the overall sequence.
While I've only played the single player campaign of StarCraft, I have studied the multiplayer of it and StarCaft II. Regardless of how the metagame has shaped up, the core design and gameplay of StarCraft is very complex, fairly balanced, and highly emergent. This is to be expected of most multiplayer games and most strategy games as well.
In part 3 I have more examples just to drive the point home.