So I was thinking about this last night, specifically in contrast with certain other FPS games this generation and how they've built variety into their gametypes by having the objective switch up every so often. I was trying to figure out how MW2 could implement something like this, and came up with, for lack of a better name, "Epic Skirmish."
6 v 6. The game lasts 7 rounds; first team to 4 round victories wins.
The first round is an abbreviated Team Deathmatch - to 5000 instead of 7500. No ties allowed. If tied after the timer runs out, you play sudden death - next kill wins.
The remaining rounds are randomly chosen from:
a) Abbreviated HQ (first to 90 with a shortened timer)
b) Abbreviated Domination (first to 90 with a shortened timer)
c) Demolition Defense
d) Demolition Assault
e) Abbreviated Sabotage (shortened timer)
f) Abbreviated CTF (shortened timer)
In case of a tie after 7 seven rounds (HQ, Dom, CTF, and Sabotage could theoretically end in a round draw), another round of abbreviated TDM is played.
Nukes win rounds, not games (actually, this may be how they work in Demo, but I've never seen a nuke in Demo before).
I'd play this all the time. Games would last a long time (thus less time waiting in lobbies!) and there would be plenty of variety. It'd be like playing a much more ADD version of Mosh Pit.