In my mind, a good game was good back in the day and still be good today. It would have the means to engage the imagination such that less-than super fancy graphics and sound would not be detrimental to game play. Of course, today there are many retro game players, many fairly young ,that grew up with PS3 and such graphics and yet they still go back to earlier games that had really good gameplay from the getgo. The list that PLM linked to is not bad, but many of the 3D games just haven't worn well. Same with sports games, but that being said I was never a fan of either or platform games too, so my list would be a bit different, but would include:
DM & CSB, Captive, Frontier Elite, the Ishar games, Time Bandits, Breach 1 & 2, Sundog, some of side-scrollers (not really a fan of schumps), Civ, Populous 1 & 2 and similar god games. Basically, when a game utilizes a fair amount of tactical strategy, it is a winner even without next-gen graphics, games like C&C, Starcraft, and the like still play really well and in many ways better than the contemporary versions of today. Dungeon crawlers too have fared well in spite of or because of games like Skyrim, whereas fast-paced FPS from the like of Doom and Duke Nukem are still games I go to over and over again, and they have big followings today! The Breach games are really overlooked, they remind me of C&C, not quite as good, but there are not may TBS around these days. And Frontier, is basically the same game as Dangerous but without needing a server and online, although that blue star field does take me out of the games way too much. At any rate, just my selection and opinion FWIW.