BO2 > BO1 > MW3 > MW2 > MW1 (I never got a chance to play WaW's multiplayer before the hacks and I never played the classics)
MW1 was the first CoD game (never owned it but borrowed it on Xbox 360) but when I first tried it (I was a Halo/Gears of War fan at the time), I could not get used to the gameplay mechanics of MW1 (CoD4) since they were so different (I couldn't get used to being insta-killed all the time and I mostly couldn't kill anyone until MW2) but I am better at CoD4 now but my memories of my bad experience for that game still haunts me as of today whenever I play on PC (I did gave CoD4 a second chance for me). While people were having a blast for Call of Duty 4, I was at the bottom of the pit. It was the shooter game that really got me frustrated back in 2007.
I am use to the gameplay mechanics in the newer Call of Duty games (between MW2 and BO2). I didn't get World at War at the time because I wasn't into the CoD series (until I played MW2) and I didn't have the money.
I am the Thunder Dragon! Xbox 360 Gamertag: TDPNeji