First: Oregon Trail (it wasn't a new game at the time, though)
Best: Too hard to pick just one. The first months of online multiplayer Quake were just frickin' awesome. Ultima Online was a lot of fun as well in its pioneering days. For single player, I think Half-Life 2.
Future: I have high hopes for Team Fortress II. UT3 will also be a mandatory buy. Nothing else is exciting me at the moment.
I know we were just supposed to pick one game for each category, but I just can't.