Cod1 was a generic shooter with cinematic SP, but with some realistic enhancements like being able to aim and actually having teamates.
Cod2 was a generic shooter with cinematic SP, but worse MP.
Cod3's SP was like it was made for kids, or by kids or something, I never played the MP much but it was pretty decent.
Cod4 was the death of shooters, the SP is cheesy and retarded, I know not everyone is some kind of hardcore military buff but it was just stupid, the MP introduced leveling which makes you feel like you're a badass when you're not. Theres a bunch of guns but most of them are very similar, theres no big maps, people mostly play for XP.
Cod WaW only played the MP demo and didn't like it, people were pissed at me for not getting this game, I saw gameplay vids of the SP and thought it was stupid.
MW2 I never played except for the demo, but it was a bigger and badder(not in a good way) version of CoD4. I keep hearing all these people yearn for the good ol days of CoD4, which was just sitting around boosting and starting all over for a little medal icon thing.
Cod BLOPS Never played it, I heard the story was alot better, but that the MP is the same old same old. However I was playing Red Orchestra with a Black Ops player one time, he was new to the game so I offered him to follow me, he said "I'll show you how Black Ops players fight" and I said "And I'll show you, how the Iron Cross is won". Before we even made it to the frontline he had emptied his whole magazine and said "I need to reload, how do I reload?" and I was like "HAHAHAHAHAHAWAHAHAHAHAWAHAHAHAHAH!"