I just played the singleplayer and Spec-ops and its pure crap.
Cons ( I would put the entire game as CON but that wouldn't be fair)
Dogs are still there (don'tcha think players hated them enough for them to be removed?)
I found it that run and gunning seemed more useful that actually aiming and shooting.
Not being able to lean to take cover makes it less useful to aim and shoot.
Heartbeat sensors are hugely over powered.
Enemies still have hacker aim but this time around their bullets are inaccurate.
AI is unresponsive at times.
Storyline is complete bullcrap.
There is no anistropic filtering options so I have to manually edit the game to so textures don't look all blurred.
Some guns (M4A1) zoom in way too much when iron sighting and make it seem like I'm using a sniper rifle.
Sniper Reticles look, odd and uncomfortable for some reason.
Fov being stuck at 65 degrees makes it hard to look around and actually spot targets.
Some missions don't give you clear instructions (SPOILER: Endgame Boat mission tells you to stay out of open areas when the entire area is a lake and the only way to really survive the chopper on your ass is to get lucky and hope he misses.)
Essential Allies are immortal so you can let them fight an entire army while you hide somewhere (present in pretty much every COD game.)
The music at times got really annoying.
ALL THE FUCKING QUICKTIME EVENTS!!!!!!
Some levels were too cramped to even get a chance to see your enemies.
Most spec ops maps are reused campaign maps (the map "Hidden" is pretty much the all guillied up map from COD4 played backwards.)
Allies seem to have really bad aim compared to enemies.
The options menu is in the Spec-ops tab (Good Job IW, because I'm gonna play Campaign on a 640x480 resolution)
No Developer console unless you get a hack.
A lot of building look reused.
Although trying to stealthing around works sometimes, its best not relied on since enemies target you like hackers.
Enemies like to run around in the open rather than taking cover like in COD4.
PROS
Virtually nothing Lol)
Less Grenade spam
Actual Physics(Its 2009 now finally they get with the program)
Maps are more complex(to compensate for that, they used low resolution textures...)
More exotic weapons (You'll still be using the same ones over and over though.)
No crossing a magical line to stop enemies from respawning(most of the time at least)
Generally you have more allies so it feels less like a lonewolf game.
The gameplay will get spiced up from time (having hostages and civilians you aren't allowed to shoot at)
Breaching is pretty fun but due to the tiny fov its sometimes hard to even see your targets.
Enemies now drop different variants of weapons (sometimes they have an AK-47 w/shotgun or an AK-47 w/ACOG.
ACOGs have much better sights.
The maps are much more open sometimes.
Stealth mission were fun so long as AI didn't bullshit you (immediately getting detected if you shot someone)
Over all this game should really be worth 20 dollars (excluding multiplayer).
Not recommended, actually I advice you not to get it at all!