It looks like the popularity of GTA IV is trailing off considerably. It's just a matter of time before it loses the #3 spot on XBOX Live. Of course, COD4's unshakable popularity is nothing short of impressive.
Rank. Game (Index)
1. Call of Duty 4 (1000)
2. Halo 3 (870.026754121)
3. GTA IV (622.16276862001)
4. Rock Band (312.59169759213)
5.Guitar Hero III (282.29912833348)
6. Gears of War (251.31613014585)
7. Rainbow Six® Vegas 2 (139.81185811686)
8. NINJA GAIDEN 2 (132.90756882713)
9. BF: Bad Company (92.862690946751)
10. Guitar Hero II (78.708897902822)
Personally, I have stopped playing COD4. While it's entertaining, it's a time latrine. After a while, playing the same maps, it becomes a mechanical emotionless process. Of course, many might suggest the same of Halo 3 or any game in the Battlefield series.
With that said, the Battlefield Bad Company demo is mighty impressive and finally feels like a proper Battlefield game on the console. I'm not surprised to see it break the TOP 10 already. We are in something of a game drought on the 360 at the moment. It's refreshing to play anyhing new.
Thank you and... don't pwn alone (tm)