The 1up post places this game under the platformer genre. As I've said before, if I gave a "genre test" to most people interested in gaming whether they develop, design, or just play video games, I believe the vast majority would fail. Like the description states, Nezumi Man is a mousified version of the classic Mega Man games (1-10). The primary function of these games is SHOOT. Sure there are some strictly platforming based challenges. But the majority of the challenges involve dodging enemies and shooting them. Also each level has a boss that you must SHOOT to kill. You gain powers by defeating major bosses and each powerup is a projectile weapon. In short Nezumi Man is an action game.
With that said I greatly enjoyed two aspects of Nezumi Man. The first is the solid design. The second is experiencing how closely the game mimics the Mega Man formula. While not as refined, creative, and amazing as Mega Man 9 or 10, Nezumi Man's enemy and level designs are smart and well layered. Some may discredit the originality of the game because of how much it borrows from the Mega Man series. But I think the game features a very unique kind of innovation. After all, Nezumi Man isn't Super Mario Bros. Crossover. With so few truly great games out there and so many games that fall short with their great ideas, I feel that more developers should copy and tweak.
In fact, I don't see much point in continuing this post. Go play Nezumi (which means mouse/rat in Japanese) Man if you like Mega Man games. It has a nifty save system so you don't have to play the whole game at once. It took me an hour and a half to beat the game. From now on, I'll group several of the 101 free indie games together in a single post when I don't have much to say about each game.