I'd really love a Mario game with high-res sprites reminiscent of the classic artworks. I don't like when games are in 2.5D and make no use of it--Marvel vs. Capcom 3 gives you dramatic camera angles during hyper combos, Viewtiful Joe has cutscenes, moves and some level designs that take advantage of it, Smash Bros. has its nifty pause screen and the way the camera zooms in and out all the time would be kind of a mess in a sprite-based game. The New Super Mario Bros. games don't really do anything that wouldn't work with sprites, so it's largely a matter of laziness...