It's a novel attempt to incorporate tried and true elements from the single player into a multiplayer mode.
On paper, it's awesome. Different weapons with different ranks and attachments. The bursts are pretty neat too, just like the plasmids from Bioshock 2.
But just like Bioshock 2, it's incredibly clunky in it's execution. In both games, the online is incredibly unfriendly to new players (i.e. starting with nothing against rank 50's). The powers almost always take a backseat to simply running around and shooting people anyways.
And just like Bioshock 2 again, it's more of a game that tests your internet connection than anything. The amount of latency is horrible, to the point where even if I shoot an enemy first with several 5.56 rounds, he can simply turn and shoot with a lowly 9mm pistol and down me in seemingly one bullet. All the touted realism of the engine had no effect in the multiplayer, as even when several bullets are fired into a foes dominant firing arm, they are still able to fire just as proficiently.
There's a lot of potential, and Rockstar was clearly banking on it (having put all of it's eggs into the DLC basket with a multiplayer focus, and zero allocated to single player), but I personally think it needs more basic fixes (balancing and netcode, primarily).
Only people I hear complaining about the multiplayer are those who are just no good at it. In my opinion it's the most fun I've had in a third person shooter, is fast, fun & frantic and very addictive. I've seen some scenes during multiplayer matches that were even better than anything Hollywood or John Woo could come up with and actually being apart of the action makes it that much more awesome.
And I like how it multiplayer once you go into slo-mo, you almost becoming invincible. I mean you're a slower target now, and you're easier to shoot at, but no, you just gained about 60 pounds of body armour for that split second of slo mo