you can play sidearms right NOW on GPengine. it is an okay game...Section Z is more betterer (or about as fun, maybe) on NES. Either way, the game hasn't aged terribly well, but you could do worse!
I am looking forward to stuff like Gaplus, Jr Pacman, that kind of thing... I hope we see that kind of stuff, it would rock!! And of course Sega 16-bit would kick ass (Shinobi, ESwat) but that is of course raher further down the road, if ever.. I mean we've not even got a solid Genesis emu at all, yet. Fun to think about though.
(other stuff that would be fun.. Robocop, Ninja Gaiden Arcade, Atari games..)