I'm posting this now before Gears of War, Splinter Cell 4, Rainbow Six:Vegas, CoD 3, and FEAR hit the 360 because the following list will surely change thanks to those
UPDATED:[11/8/06]: #1. GEARS OF WAR[360] *The other 9 don't even compare*
#2. Splinter Cell:Chaos Theory [Xbox]
#3. ElderScrolls 4: OBLIVION [360]
#4. Splinter Cell [Xbox]
#5. Code Veronica [Dreamcast]
#6. Condemned [360]
#7. Ghost Recon Advanced Warfighter [360] (Single Player)
#8. Tomb Raider Legend [360]
#9. Tomb Raider [Saturn]
#10. Shadowman [Dreamcast]
#11. TIE: Splinter Cell: Pandora Tomorrow/Sega Rally 2 [Dreamcast]
#12. Call of Duty 2 [360] (Single Player)
#13. Unreal [PC]
#14. Tomb Raider II [PS1]
#15. Americas Army [PC]
#16. Aliens Vs Predator [Jaguar]
#17. Unreal Tournament [PC]
#18. Fable [Xbox]
#19. Silent Hill 2 [Xbox]
#20. Powerslave [Saturn]
#21. Rallisport Challenge 2 [Xbox]
#22. Brute Force [Xbox]
#23. GUN [360]
#24. Soul Calibur II [Dreamcast]
#25. Medal Of Honor [PC]/Goldeneye 007 [N64] TIE
#23. Rainbow Six III [Xbox]
#24. Morrowind [Xbox]
#25. Ninja Gaiden [Xbox]/Manx TT [Saturn] TIE
Honorable mentions...
Alone In The Dark The New Nightmare [PC]
Morrowind [Xbox]
Ninja Gaiden [Xbox]
Manx TT [Saturn]
Panzer Dragoon [Saturn]
Tomb Raider III [PC]
Fatal Frame 2 [Xbox]
MYST [Saturn]
DOOM III [Xbox]
Ghost Recon [Xbox]
Duke Nukem [Saturn]
NiGHts [Saturn]
Mortal Kombat II [Snes]
V-Rally [PS1]