They are all bad. Small maps, annoying kill streaks, arcade knifing, lag, campers, kids, hackers, linear campaigns, annoying music, quick scoping, auto aim, killcam, cheesy zombies.
COD4 and Modern Warfare 2 are the best because the original InfinityWard Team now (Respawn) made these games.
Everything else is repetitive, flawed with imbalance.
At the very least play the entire COD4 single player campaign.
It still holds up against everything today with epic moments and well done story line.