Yeah Bayonetta is awesome too and I feel stupid for not mentioning it. It's leagues better than the DMC series even and DMC is one of my favorite series. It also runs way better on 360 unless you get the patch for the PS3 version, then they run about the same (360 version is still a little less choppy).

Guardian Heroes is coming in a few months (I think, unless they moved it forward) and it's one of the best side scrolling beat-em-ups ever, and even has some RPG elements. There's a pretty good reason why the game goes for over 100 bucks on Saturn.