So do you mean like console games or old PC games?
If we're talking older PC games probably Mabinogi. Having an offline client that is seperate from the MMO would be pretty cool, especially if it's tweaked to make the combat work like it used to before dual swords became the default cheese.
If we're talking console decomps, native decomp ports of Skate 2 and 3 would be amazing, especially if it's built with mods in mind XD
The skate online thing is such a dissapointment and just makes me want a PC version of the console skate games more.
Oh yeah! just because I just remembered it Dargalia Lost as a full screen PC game would be so awesome :D
(on a side note ugh my internet connection is so dogshit I might as well be using dial-up right now)