Endless respawn was silly, but it wasn't broken. No more endless respawn, no more challenge.
But, I do think the cover plays a rather large portion of it. You have to remember, the cover art is likely the first thing seen by more or less everyone at the store. You see a cover, you see two things, the name and the art. You see action, you unquestionably think action. You see say, Battlefield, you realize "Oh hey, this game has tanks in it!", dead center. You then proceed to decide "Do I like tanks?". So on, so forth. The older CoD's cover makes you feel like there is something to be done, some evil to exterminate right there on the cover.
If you look at just the pictures, no names or text, it's clear. That also falls in line with Activision more or less saying "It doesn't matter in terms of quality or completeness, the people want Call of Duty", as you will also note the text becomes a bit more prominent in terms of focal point. Atleast to my eye.
The MW2 on covers don't make me want to go blow something up. They dont make me want to "strap on my combat helmet" so to speak. So regardless of weather or not the cover is solely to blame, it certainly has an effect at the end IMHO.
@Zak - The other day someone seriously brought up Mechwarrior at work. I was like "Waaaaaaaaaaaaaaaaaat?"
I'm also sure BF is exempt, as they also feature vehicles, which pollutes the issue I am sure. Also, BC2 had the cliche soldier action and still turned out pretty fine.