Please bear in mind that I do not think of these games as "bad". both games are factually brilliant at being interactove media and well designed out the ass, but i'm sick of them. This sentiment actually goes a lot further than  just COD and R3, because it's what they inspire that I dislike; I'm a pretty damn good consumer. I buy most games at or damn close to release, complete them and maybe do a little achievement mop up and then BAM I'm finished with it and it sits on my shelf for when I want to play it again or lend it to friends or whatever.
What I dislike is the kind of single-mindedness that the games produce in the entirety of my friends lists. Every night at least 75% of my friendslist is playing through private games of one or the other. Sure, I agree, the games are super fun and I join in with the games for so long as I can stand it, but dude! there's a limit to the amount of content that's actually in the game, do we really have to play Rust again? isn't Fort Mercer kinda boring?  Can't we, you know, play some Left 4 Dead or Crackdown 2 Demo? No? awwwh...
I've never been one who enjoys a grind. it's the reason I only periodically play Forza 3, it's the reason I never S-Ranked Just Cause 2, It's why I think so poorly of FF13. Games have to be fun to keep my attention and Co-op is where the fun really is nowadays, whether that's because of a meta game, like homebrew VIP or Left 2 Die (alternatively, Realisticly Left 2 Die Too) or just because it's balls out wacky, I'm annoyed that it's being ruined by admittedly fun games with stupid-ass grinding. 
 
Edit: It appears I can't spell and made Red Dead R3. Dunno how that works, but It's staying. GOTTA COMMIT!