Hmmm been playing for a solid 5 hours or so and am on rank 35/80 - Much faster ranking up system than BF as per previous COD's.
I'd have to say that even though it is a great game for mindless run and gun fast paced, killstreak based killings, my heart still tells me to play BF3.
When I first started playing the MP, the first thing I said to myself was "Holy shit this is COD4". Which pretty much sums it up.
VERDICT:
Good game, feels a little too familiar to COD4, just with more guns and gadgets. Rather stick to BF3 and just play MW3 on occasion with friends or for mindless slaughter.