When I want to know how good a game is I'm pretty much a slave to GameRankings.com. Since they combine all the reviews out there, it's usually a pretty good indication of how good a game is.
You can sort by just Xbox, and by year and other criteria.
The top 20 Xbox games, according to them, are:
1. Halo: Combat Evolved
2. Halo 2
3. Star Wars: Knights of the Old Republic
4. Grand Theft Auto Double Pack
5. Ninja Gaiden Black
6. Tom Clancy's Splinter Cell Chaos Theory
7. Burnout 3: Takedown
8. Project Gotham Racing 2
9. Prince of Persia: The Sands of Time
10. Forza Motorsport
11. Grand Theft Auto: San Andreas
12. Tom Clancy's Splinter Cell
13. Tom Clancy's Splinter Cell Pandora Tomorrow
14. Ninja Gaiden
15. Soul Calibur II
16. Psychonauts
17. NFL 2K3
18. The Elder Scrolls III: Morrowind Game of the Year Edition
19. NCAA Football 2004
20. Half-Life 2
Below is a link to their Advanced Search. Just change the "Platform" to Xbox and the "Limit results to" to 200 if you want the full list.
http://www.gamerankings.com/itemrankings/simpleratings.asp