I didn't put BO2 in there simply because I haven't played it enough to rank it. The game is a lot of fun so far but there are a couple of things that need tweaking and I want to see what direction Treyarch goes in to fix these problems.
It's going to be hard to beat BO1 though.
I'll admit, I spent more time on BO1 than any other Call of Duty and, while at the time I thought it was bland, I never really knew how much I appreciated that game. It felt slower, but I truly enjoyed that pace and wish BO2 had the same feel.