It is my personal favourite for roleplaying in, as it has a unique flexibility found only in simple games with simple rules, that allow themselves to be twisted and distorted to you heart's content, and also even distort themselves as examples of how easily they can be changed to completely switch somethin in the book with something of your own devising.

 Add to that the fact that it can do anything that any other system can do, except simpler and in many cases better, and you have a truly remarkable system to use for, well, anything, any genre (not just anime), and any setting, ground, or game.