You know what? I don't get it.
I finished playing CoD 4: MW about a week ago, and since I liked it very much, I purchased MW2 a few days later... And I liked it more actually. True, the plot has an uncomfortable level of holes in comparison to it's predecessor, but gameplay wise? What was working (great firefights, amazing feeling of tension, overall epicness), remained, and they added a few more 'awesome' features, like that snow mobile part in the first mission with Roach, and many other things like that.
I didn't play BlOps yet, but so far I'm scratching my head about this whole 'losing it's charm'. Granted, I never played a CoD multi (except from CoD 1, which was a ton of fun actually, but I'm talking about the latest installments), so maybe the problem lies here, I dunno...