I don't know about you guys (that is if you have played it) but I personally believe this games online is miles ahead of Modern Warfare 2!
The maps are vast, the vehicles are very reliable, and the weapons test your aiming. Sniping is a dream, there is no holding of breath or shaking.
NOTE: this game isn't for everybody, being as online play is harder than MW2, do download the demo or rent before purchasing if you aren't familiar with the series.
Also, I don't know if there are any JRPG fans here, but I just picked up FF XIII and it is amazing!