I wanted to try to offer a more critical review than the either glowing 5-stars or completely ignorant 1-stars. I will preface this by saying I got this game for a little less than half price from a friend, the day after release. I will get to the reasoning for that shortly. Game is WELL worth the price I paid, however if I had paid full price...I'm not sure I would feel the same. The lack of matchmaking in Co-Op, and some poor multiplayer choices are what prevents this game from being so much more.
I have not gotten very far into the single player, so I cannot comment too much on it. As others have said the story will definitely not blow you away, but I feel the gameplay is enough to make up for this. The tactical/stealth ability is enjoyable to play, but you can also use a run and gun style of gameplay if that is what you prefer.
Guerrilla mode is an awesome addition. I can't help but love any type of "horde" game mode (zombies/survival/you name it). However, as others have mentioned, the lack of matchmaking for the Co-Op game modes is a HORRENDOUS oversight. There is no justifiable reason to make the Co-Op modes strictly invite only, and is easily deserving of a one star reduction.
Now to the multiplayer. Overall thoroughly addictive and enjoyable gameplay. GR veterans will find that although it is definitely a departure from the series, there are little details that will bring back fond memories. The graphics may be viewed as slightly under par with other recent releases, but the game looks amazing on my screen, and the realism of character movement is impressive. I will say that it is NOT an easy game to play, and those who can't pick up on the style will be smacked around mercilessly. I count this as a pro and a con. I personally love the extensive use of cover style of play, however that is the style you MUST play in. Any thought of not adapting to this style will result in a completely unenjoyable game experience. For those who dig it, you can become a veritable killing machine once you pick it up. Unfortunately, you will find that this style can (sometimes) result in a total deluge of campers, who would rather sit behind a concrete barrier and wait for passersby than to actually get up and go after the objective.
The multiplayer cons are what bring the game down most for me, and also the reason that I was able to get the game so cheaply. In the GRAW games the host was able to choose the map, time limit, and weapon kit. This is gone. I'm sure private games still allow map and time selection, but the kit option is gone entirely. What you get is a choice to vote for one of two maps. Way to dumb it down Ubi. For those who are new to the GR series this may not mean much, but to the veterans, especially from GRAW I and II, this is everything. If you played GRAW II recently you would be lucky to find a sharpshooter (team deathmatch) player game running, but you could ALWAYS find a Pistols Only Blind Siege ranked game. These were/are the hardcore players who still played the game years after release. Kit selection is gone, blind siege is gone, sharpshooter is gone. Some have said that team deathmatch would be added, but why would it not be included in the game upon release? It makes no sense, and leads to one star reviews with people whining about "no team deathmatch?". Some will mock those who say that, but the fact remains that team deathmatch is the industry standard. To leave it out, or to intend for it to be in the game but not upon release, just makes no sense. The load times can also be extremely long at times, and I have had issues with losing connection to the server before loading the lobby and after entering the game.
I will be getting more into the singleplayer and Co-Op modes, and will edit/update this review as necessary. I was really hoping for this game to be a home run, but it is more like a double. Worth checking out, but I would rent or try to check out the gameplay first, so you know what you are buying.
* Update 6/01/2012 *
Single player is a little too linear as compared to previous GR games, but I enjoy it. The rendering of human faces in cut-scenes is really, really poor, as mentioned by others. Like they spent so much time making characters with masks look bad*** that they completely forgot about those not wearing masks or helmets.
I love the multiplayer experience in this game, however, major server issues are dragging it down. Almost constant issues with losing connection to servers, host migrations, lobbies that won't start, and lag that is absolutely ridiculous. I've shot a guy with two full clips who didn't even seem to notice my presence, and then he dies ten seconds later. No exaggeration. Hopefully they will get these issues ironed out in the coming weeks. It should also be pointed out that the info on Amazon states 16 player multiplayer or 8v8, when this is not the case; the multiplayer is 12 maximum.