BioShock is a highly immersive and extraordinary experience that even casual gamers will appreciate.
The game features a unique combat system in which you combine both magic (known here as 'placids') and physical weapons, using them to your advantage to erase your opponments at all cost. The average enemy you can face as though it was a game of Call of Duty, and shoot at any means nessecary, but the primary antagonist known as the Big Daddy requires careful planning and risky decisions upon how you decide to approach them.
As many have mentioned, the game's ultimate factor is it's immersive world. To back this up, it contains some of the most beautiful, yet grittiest scenery you'll find in any game for years to come. It's a dark, grotesque game, that simply places it in a sub-genre of horror.
Theres a wide variety of weapons, from placids, guns, close-range weapons and even the enviroment gets involved. How you decide to dispatch your enemies is entirely up to you, as there are hundreds of ways you can do this. You might want to kill them simply Halo style. You might want to get up close and personal with your pliers. You might want to electrocute or incinerate them to their death. Or hows about be original and combine them all in once. Set your enemy on fire, and whilst he's burning alive, put a few clips in him so he's on critical health, and whilst he's helpless, put him out his misery with a swing of a wrench.
There isn't any disadvantage I can think gameplay wise. Playing the game will simply take your mind of any bad points anyway. The one thing I can recall as a disadvantage is simply the replay factor. Once you've finished it, there's probably no going back. I feel it's one of those games that is a truly incredible experience whilst it lasts, but you just simply can't play it again. Unless you're an achievement freak, go ahead.
Overall, BioShock has to be experienced no matter what genre you're into. There's little to fault here, maybe the excessive wave of enemies that don't seem entirely necessary, and the level design can get repetitive pretty quickly. But with storyline that more then makes up for those minor flaws (and then some), BioShock delivers on so many levels its hard to keep track of them all.