The classic Top 10 for me:
1. Wolfenstein;
2. Wolf3D;
3. Worms;
4. Mario Bros;
5. The Galaxy Game;
6. Pong;
7. Mortal Kombat;
8. Prince of Persia;
9. PacMan;
10. MIB (Men in Black). (a nice 2D maze type game, no reference about it found
)
The all time Top 10:
1. Starcraft;
2. Half Life 1;
3. Counter Strike 1.5;
4. Lineage series;
5. Warcarft series;
6. Command and Conquer series (damn those ships from Red Alert where nice);
7. NFS: Porsche
8. Condition Zero;
9. Team Fortress;
10. Alien versus Predator (the classic version).