Alright, here's my review as promised (prepare for a wall of text!):
THE GOOD
The enemy AI is very well done. Enemies will only run out of cover if they know they are being flanked or are otherwise in danger of dying (this is on contract aka normal mode). They even wait until you reload or get distracted to pop out and fire, otherwise they pretty much just blindfire. If it is obvious that you are in a tight spot, they will rush you. I doubt I'll play this on single player anytime in the near future so I can't comment on the partner AI (reports seem mixed).
Weapon customization is freakin' sweet. I didn't think it would be that big of a deal, but I find myself getting a bit giddy when I know blowing up a chopper might net me that little extra boost in moolah to put a freaking shotgun frontmount on my sub machinegun. Yes, you read that right...A shotgun undersling for an SMG...Awesome.
Co-op moves are great and not forced like I expected. You don't have to co-op snipe if you don't want to and back-to-back moves are nicely sprinkled throughout the missions without being repetitive.
Story is alright I suppose. It is a little weird seeing 9-11 in a video game or a suicide bomber yelling out "long live Saddam". Maybe a bit too soon? I don't know. I'm on the second to last mission but if I'm right the plot twist can be seen from a mile away. No one cares though since you most definitely did not buy this game for the story. Let's be honest here.
Most importantly, level design is top notch. The forth level was freakin' brilliant. I think any action gamer will appreciate how it ends. There might not be a lot of levels but so far they have been very varied and open. Think of it kind of like Halo or Gears. Sure it is linear, but you have options on how to tackle each battle with cover strewn about and flanking moves available here and there.
The cover and Aggro system also work exceptionally well. I hope all games use this cover system because it is so effortless and intuitive (no button input necessary). Aggro works like it should and overkill modes are freaking fun.
Can't comment on replayability yet, but it looks to be decent.
THE BAD
The game suffered from a bit of lag during my first session with occasional hiccups and freeze frames. When the game starts to chug, the fun gets zapped out real fast. Hopefully this won't be common. Fortunately, the lag seemed to even out and fade as we went along. Still, it was highly annoying when it happened.
Also beware this game drops f-bombs like no other. It probably puts Butcher's Bay and Gears to shame with the language. I don't mind it per se but it does seem rather superfluous.
I found ammo pick-ups to be somewhat of a problem as well. I was super pumped when I brought in my RPG for the first time, but after one shot I NEVER found another round all mission. WTF? Same goes with the sniper rifle. These weapons are the most fun, so why can't you use them more? It seems that you can only find ammo for your primary and secondary weapon (sidearm). You also cannot pick up enemy weapons which is kind of lame.
THE UGLY
Expect some texture pop and lazy modeling (mostly on background objects and environments). The character models are very detailed however, so it is somewhat of a trade-off I suppose.
Loading times are downright cruel. Expect 20-30 seconds of waiting when going to buy weapons, loading up a level, or just about anything else.
I guess in conclusion it's about right for the scores it has been getting and an acceptable replacement of/compliment to Gears of War co-op. It is definitely a solid title with some great mechanics. A little more polish would have been nice but I would say it is already above average as is. Again, I must stress that this game can only be fully enjoyed with a friend! Any other way and you are just doing yourself a disservice.
It's as good as I thought it would be and the perfect game for my brother and I. I'm glad I bought it. Can't wait to finish it tomorrow and get working on buying that minicannon and grenade launcher!
ing kidding me. 
