No surprise BioShock 2 picked up an M from the ESRB, but that's not to say its newly minted rating certificate isn't interesting. The writeup says we can expect F-bombs, mother F-bombs, the C-word and the past tense of "tweet."
There are some minor spoilers in the writeup, I suppose, so I'll let you venture over there if you're interested in what the awesome displays of violence entail, as they most directly pertain to capabilities or plot points in the story.
"The violence and the profanity account for the Mature rating," saith the ESRB, so let's look at the other half of that equation.
The game includes frequent use of strong profanity (e.g., "f**k," "motherf**ker," and "c*nt") and some lesser four-letter words (e.g., "sh*t" and "tw*t"); in one instance, an enemy attacks [Subject] Delta [that's you] while screaming, "F**king sodomites everywhere!"
Sodomites? F—- yeah! Oh there's also some stuff about hookin' and red-light districts. Frankly, in a laissez-faire capitalist society I'd be astonished if those weren't encountered, so maybe this should be rated O for Objectivism.
BioShock 2 [ESRB via Hot Blooded Gaming]