A close second in the ranks are the Desert and Jungle Strike games. These hard-as-nails shooters were awesome back in the day, and they really stand the test of time. Mutant League Football - which is basically the classic Madden NFL played with monsters and various field obstacles - is also a fantastic little title that's made even better with the wireless multiplayer option.
After those six great games, you have six not-so-wonderful selections, though a few of them are very creative and still worth playing. Virtual Pinball; side-scrolling jump-and-shooter B.O.B.; fighter Budokan and the "you're a ghost" action adventure The Haunting just look and feel as old as they are. The Haunting is still interesting, though, just for the neat scare-tactics gameplay. Isometric squad-shooter Syndicate and RPG Ultima VII are both emulated versions of the less-than-stellar console ports, and not the original PC games, and thus are pretty lackluster.