2D gaming is great, but I think the consoles can take this to their advantage. 2D games were restricted in their size, diversity, and control. With the next gen of systems, we have more freedom than ever. Imagine playing a Mario game that encompassed the whole world rather than a kingdom. Instead of 20 levels, you could have 100, possibly more. In addition, we have the power of "saving" these days, so having games these large won't be a big problem for a gamer trying to beat them. I also think we can always tweak 2D into 3D, sort of what we like to call 2.5D. Viewtiful Joe is a great example of that because they used the side-scroller and added the 3D power the Gamecube can pump. The thing I want most is diversity in characters. In the Nes and Snes games, we'd just have to beat up like 500 clones of character. I'd like to beat up 500 different looking individuals.
I'd really love to play like a 200 level Ninja Turtle, side scrolling game, which would have lasting abilities.
One thing that could be cool for future online games is this: A 32 player wrestling royal rumble in 2D!!!! Or even LAN. A machine this age can easily run at 60 fps with all those characters fighting each other.