Halo 2 in the lead.
GameRankings.com rank games according to the reviews in major online publications. This is recent chart for top Xbox games 2004 (updated December 26):
Top 10 Xbox games 2004
1. Halo 2 Microsoft 95.5%
2. Burnout 3: Takedown EA Games 93.7%
3. Tom Clancy's Splinter Cell Pandora Tomorrow Ubisoft 93.1%
4. Ninja Gaiden Tecmo 91.8%
5. ESPN NFL 2K5 Sega 91.1%
6. Madden NFL 2005 EA Sports 89.6%
7. Rallisport Challenge 2 Microsoft 89.5%
8. Star Wars Knights of the Old Republic II: The Sith Lords LucasArts 89.3%
9. The Chronicles of Riddick: Escape From Butcher Bay VU Games 88.8%
10. NCAA Football 2005 EA Sports 88.7%