I-Ninja
I-Ninja is loud-mouthed, rambunctious, and full of rage and wanton violence. He's the worst ninja ever. But, he's pretty fun to use as a means of slicing guys up. The game's failings are clear from the outset, but there are a few things it does pretty well.
Combat is simplistic, but not without merit. In addition to just running into guys and slashing around, there are certain scripted encounters with miniboss-type enemies which will place Ninja and the baddie in an anime-styled action tube, with leaping and slashing and so forth. There are also some environmental puzzles ala Prince of Persia (though not nearly as impressive). The level design is somewhat eye-catching, if a little monotonous; the enemies use robots and have control panels everywhere, so a lot of areas look the same.
There's even some character growth, though in the end it's somewhat disappointing. Ninja receives sword upgrades based on the amount of enemies he's killed, but you'll have the final sword long before you even have access to the last levels of the game. You can also get health upgrades by earning new belts, which in turn are from completing more levels, but, more importantly, you need higher belts to access new areas. And, apparently, someone decided that playing each level once isn't enough to proceed; each level has multiple 'grades' you can earn (by doing alternate challenges like a time attack, or collecting red coins, or defeating all the enemies), and you'll need to do these to open up the game farther. This is what's kept me in what I believe is the final area of the game, without the impetus to finish it up.
Progress: Moon Base