I played MW2, it's great and all, the multiplayer is fun but I can't say it's better than Halo, I just can't.
I don't know, for me the gameplay is a lot more fun in Halo, what with the nice vehicles, the grav-jumps,
the pull-to-enemy-melee's, swords

, and Forge too.
Me and my friends made this arena game, you have like 1HP, you go into the arena as fast as you can, get into the cages and stay there (the cages protect you from bullets), so the only way you can get killed in their is if someone comes in your cage and shoots you, or they have to time their melees just right when they get in. I don't know I just thought that was really fun heh.
The reason I don't play MW2 a lot is because people are just total losers, especially when it comes to camping.
If you think people take Halo seriously, think again, my god I swear some people have a k/d ratio of like 4.1,
seriously I really don't think they ever get out of the house >_>
And apparently there's this stupid teleport glitch, pretty damn annoying.
However the maps on MW2 I must say look a ton more l337 than on Halo, but still for me, Halo's got a ton of replay value.
Maybe it's because I only play MW2 at my friends house...........so I don't play it very often to achieve it's somewhat replay value better than Halo's.
All in all I can't wait to play Halo Reach when it comes out, and Puncharger, I bet all my life savings you will get it too.