The critics cannot possibly have their review right on this one.
Highly addictive multiplayer is what makes it for me, along with its superb graphics and lovely level design. Although the game does not have an actual story-line, it has a lengthy, enjoyable, and rewarding single player 'Infinity Mission', which I have been playing for 10+ hours. The difficulty levels are perfect ie: easy is easy, hard is hard, etc. The whole idea of this single player, is to train and recruit new soldiers, which you split into squads for multi player use.
One thing that I did not see coming when I started the multiplayer, was the fact that you can lose your soldiers obtained in single player, if captured by the enemy team, if the server mode is RC (Real Combat). There is also standard VR mode, where you cannot lose your soldiers.
Another surprising aspect of the game was the included Boss-Rush mode, where you can challenge all of the bosses from the original MGS: PO, with no risk of losing obtained soldiers. Correct me if I'm wrong, but in the American version, you must import a game save from the original MGS: PO to unlock this feature, whereas the Australian copies (mine) come with it included.
Altogether, an addictive multiplayer game, a nifty little (yet challenging) single player addition, and with superb graphics, amazing sound effects and a heap (68) of characters make up for a great portable gaming experience.