It's hard to compare KZ2/CoD5 (don't have CoD4), they're completely different games.
I've been playin KZ2 more lately. While it's really fun, there's alota things I don't like about it.
When it comes to Search and Destroy, it's horrible in KZ2. I mean completely stupid. The bomb is usually always placed right next to the defender's base which means they obviously they had Tacticians in mind. Both teams usually place spawn grenades right next to the objective. The result is 5 mins of the some of the most braindead action you'll ever see in an FPS. You got people spawning right next to eachother and both teams throwing grenades right on the bomb area so it's nearly impossible to plant. It gets repetitive and old.
I find KZ2 most fun in matches with less people - I stopped joining the 32player games a long time ago. While this game is also really lacking when it comes to weapons, the few that it does have are some of the best I've ever used. They have a great feel to them. Much better than CoD5's, which feel more like automatic capguns that you'd buy off an ice cream truck. Some of the classes are pretty fun to use, but a few could use fixing - the balance feels abit off, and the game's ribbon system was obviously given very little thought.
As for CoD5, it's abit more braindead than KZ2 but I still like it alot. After playin KZ2 for a while, the party system and responsive controls are much appreciated. The thing I hate most is the lack of skill it takes to get kill stuff - you can get so many lucky bs shots in that game. The rifle grenade is also stupid, but not as bad as KZ2's Assault class (glad most people disable it anyways).
There's alot I can say about both games, good and bad. I play KZ2 alot more only because I've had CoD5 since release (little bored of it), but it's hard to say which game I like better. I might have to go with CoD5.
As for Halo3, I've never played it but based on what I know, it's a million times better than CoD5/KZ2 when it comes to variety and options.
