The single player in black ops is so bad you can get through the entire first mission on a harder difficulty without firing a shot. Except in certain enforced scenarios. All the parts that even in other examples of the genre would be "shoot or die" areas you can just sit behind some cover with your head down and your AI partner shoots everything out pretty quickly.
I've watched people play. I've attempted to play black ops on a 360, but I'm still bewildered as to why anyone would choose the horrendous handling from a gamepad compared to keyboard and mouse. I shot the sky a lot and died a lot. It was boring.
I've played through about 1/3rd of CoD4 (I got CoD4 and CoD4:MW2 whilst on offer purely to see if they did offer anything, since they're so popular) and I honestly couldn't tell whether it was a tongue-in-cheek comedy or just a really badly done "WAR IS GLORIOUS" game. The cutscenes are absolutely dreadful, if it really is a "WAR IS GLORIOUS" (which I suspect) then the cutscenes are less believable than the infamous FFX laugh scene.
That would maybe be forgiveable if the game itself wasn't so buggy and broken. Getting stuck on a railing when you're 2 metres from it during a timed section causing a death followed by spawning right next to it afterwards (thankfully
just far enough away to not get stuck on it again) isn't exactly conducive to a fun gaming experience.
Talking of spawning in stupid places: I was mucking about with a car, shooting it up whilst standing on top of it. Unrealistically, but in line with hollywood, it exploded and killed me. So I respawn on top of the car again, whilst it's already alight. Managed to escape before it went boom though.
The AI is absolutely dreadful in it. When it's not busy shooting everything in sight so you don't have to bother (I might try and do a mock Let's Play of the entire game where I just run through and never use my gun unless directly ordered) then they're standing in doorways so you can't get past them or running in front of grenades.
I kid you not, I had this happen: 2 enemies in a small room I had to run through, I was stood by the doorway, 2 AIs. One of them ordered me to throw a flashbang into the room, so I backed up a little and literally as I brought my arm back to throw it, the other guy dived in front of me, walked just past the doorway and turned round to look at me. I'm still WTF-ing at this point and throw the flashbang, it bounces off the guy, knocking him further into the room, where he gets peppered with fire so runs back out, just in time to watch the entire team get flashbanged. Thankfully the enemy AI wasn't clever enough to run out and kill us all in the meantime.
Had I been taking the game seriously, I would have been pissed. Instead I was pissing myself laughing.
The AI is terrible. And that's from someone with 170 hours of Left4Dead gameplay. At least you can push them out of the way in L4D if they insist on standing in a doorway.
So, those are my CoD4 experiences summed up from a few hours of playing. I keep intending to play some more, but I need to be in a really good mood so I can see the humour in how bad the game is.

As I said previously: I could write a thesis on the bad game design decisions in the game.
If you want to laugh at just how silly even others in the industry think it is, take a look at the parody "Duty Calls"
http://www.thedutycalls.com/And a playthrough of said parody:
http://www.youtube.com/watch?v=eE_msAKWdOs