I've always said I liked the 2D aspent of older games/systems a lot more in many ways.
1) Easier to play, casual fun with less learning curve
2) Not so straining on your eyes and senses. 3D is so hard to navigate, a lot of effort goes into just moving around and trying to remember where you are. Makes me a little head sick actually.
3) The forward/back feels more adventuresome, like you are always waiting to see what's coming at your next - with no way out.
4) I loved Castlevania games in 2D, awesome - I'd love a 360 version of one of them.
5) Simple nastelgia (yea, I can't spell) would make me interested in a good, 2D game. Or the Abe's Odysee games were great as well in 2D.
Do it! 3D and multiplayer online are both over-rated, I never play games online...don't care about that.
And while you guys are at it, stop making games so complex and simplify your menus. I don't want fancy menus for god sake. Just press play or load and make it fricking simple and fast. I have vbery little time for gaming and the complex games don't get played.