I played all three a decent amount. Currently own 2/3. Killzone 2 and MW2.
Killzone is just beyond dull, the game just lacks a lot of key elements for me to like it, a mix of controller, maps, characters and overall fun factor.
Battlefield:BC 2on the other hand is just a better game than MW2.... but not better than COD4. The reasons why Battlefield is better is simply put that teamwork is vital, and it brings better maps, playing atmosphere and fixes a lot of problems that MW2 has.
The problems with MW2 is that it has so many issues with actually being able to play the game perfectly, that you just end up hating it. Also the maps aren't as great as the first.
Killstreak also makes it really pro friendly (what do I care, I am pretty good at the game).
