GRAW is an absolutely amazing game with a frustratingly incompetent AI that almost ruins the entire experience.
Almost right off the bat, G.R.A.W. completely immerses you inside of the game world. There are not cutscenes, no FMV sequences. Every bit of the game takes place in the 3rd person perspective that it is played in. All of the story elements are relayed to the player through a video window in the HUD. Mexico City is about as real as a city gets inside of a game. Buildings are rendered for miles into the distance. Heat shimmers off of surfaces and affects your view. Pollution clouds taller buildings. Transitions between levels all take place in real time, interupted by only a brief loading screen. When you are transported to a new location in the city, you actually fly to that location. These are some of the most stunning visuals in the game, with the entire city layed out below in fantastic detail.
The game controls almost perfectly. Controlling your character, you actually feel like he is the elite soldier the game tells you he is. Taking out enemies from behind cover, calling in airstrikes, diving across enemy fire, it all controls incredibly fluidly. Animations are smooth, and all of the characters movement look incredibly realistic. Levels are huge and varied. In fact they're so massive that you'll often end up passing by buildings or skyscrapers that were so distant at the beginning of the level that you thought they were only scenery. Levels are laid out well so that enemies are challenging but not impossible to overcome. Furthermore most levels make good use of height, proving that most of the buildings are there for more than just looks.
I can't comment too much on the online play, since I didn't get too deep into it. I did play a few rounds though, and overall I wasn't all that impressed. The visuals are dialed down significantly in the online play. So much of what makes the single player so impressive is stripped out that it almost looks like and entirely different game. Presumeably this is the make the load easier on your bandwidth. However, I still ran into a lot of problems with lag.
My biggest gripe with the game though is not the online play but the AI in the single player. For me, this nearly ruined the game. To put it simply, the AI for your squadmates is abysmal. Babysitting your teamates becomes an excercise in frustration. The step out into enemy fire. They ignore orders. Rocket launchers will shoot other teamates in the back. They'll get stuck trying to get around corners. G.R.A.W. has some of the worst AI I have seen since the PSone era. What makes it even more confusing though, is that enemies don't seem to have the same problems with their AI. If enemies can competently take cover when under fire, why can't allies?
In conclusion, it's hard to know how to recommend G.R.A.W. If you can overlook the AI difficulties, you'll find an incredibly smooth and polished game. However, if you're the kind of person who gets frustrated easily, you'll be breaking controllers by the second level.