We've seen a string of successful digitally-enhanced remakes that play like the originally but look a lot better. The Tales of Monkey Island immediately comes to mind, and the more recently released Ocarina of Time has also proven to be a huge hit. Personally, I'd love to see the earlier Final Fantasy games re-mastered -- keep the stories and game design as they are, but give the graphics a 2011 make-over.
How about you? Which game(s) would you like to see given a graphical face-lift?