Half-Life 2 in the lead.
GameRankings.com rank games according to the reviews in major online publications. This is recent chart for top PC games 2004 (updated December 26):
Top 10 PC games 2004
1. Half-Life 2 VU Games 96.5%
2. Unreal Tournament 2004 Atari 93.2%
3. World of Warcraft Blizzard Entertainment 92.9%
4. Rome: Total War Activision 91.3%
5. The Sims 2 EA Games 91.0%
6. The Chronicles of Riddick: Escape From Butcher Bay - Developer's Cut VU Games 90.5%
7. Far Cry Ubisoft 89.3%
8. Tiger Woods PGA Tour 2005 EA Sports 89.2%
9. Doom 3 Activision 88.4%
10. Sid Meier's Pirates! Atari 88.0%