I've played both CoD2 and CoD5:WaW online with great pleasure, but I must say the longer I play CoD6:MW2, the more I appreciate the former two.
Reason: no dedicated servers.
For any multiplayer newbies here: that means you are
1 - randomly teamed up with other members who may be a thousand times better than you are so that you end up with a 1/1000 kill/death ratio
2 - there are no moderators, which means you usually don't last longer than 10 secs before some bunnyhopping spawnkiller backstabs you
Even better, if you've earned an airstrike or another similar killstreak award, in the 2nd round of a game you can immediately order a strike directly over the enemies' spawnpoint getting dozens of kills with absolutely no skills whatsoever
I think I'll be moving back to CoD5:WaW soon...