Call of Duty 4 pretty much defined the modern combat genre. Its close to perfect, which is why MW2 and Black Ops are terrible by comparison. You can't get any better than it, so releasing another "ultra realistic" shooter, or another "CoD4 with a bunch of extra crap" isn't going to do anything.
You need something completely different. Redefine the gameplay. Halo, Gears, TF2, all of them are successful because they aren't another Modern Warfare.
On top of that the perks allow you to engage your enemies at lightspeed. The game itself became too easy which is probably why the devs included the 'Pure' mode which is more like multiplayer pre-COD4. Now, most people would be fine with all this if BO didn't have as many issues as it does.
But I do agree with you that CoD4 was the CoD franchise in it's prime now multiple spinoffs are turning this into something very ugly. This is why I'm excited for BF3 as it's returning to its roots. More or less refreshing BF2 instead trying to make it completely different.