I will start by saying that I have played a lot of this game. I have played about 80 hours over the past year or so, and I have periodically gotten bored of it and quit, but I always end up coming back. It is really fun and engaging, and there is a nice community if you use the chat rooms/multiplayer. It also is quite violent. The violence is on par with other M-rated titles like Call of Duty and Fallout, but it is zoomed out a lot, so it is not quite as personal as first person shooters.
It is also surprisingly not sexual. Most developers tailor to the main demographic of games (men) by adding lots of scantily clad female characters to their games. I don't mind the sexuality as much as I mind the fact that it is a blatantly shallow and stupid way to advertise your game. This game is different. You can play as a female character, and the most sexual thing about it is that you start in typical raggedy cloth armor like everyone else.
BUT: The main thing to be advised about this game isn't the violence; it's the commitment. It is a very hardcore game that wants you to spend hours upon hours grinding for equipment. The story is pretty lackluster, and you finish it in a matter of a few hours and move on to the real "meat" of the game: replaying various quests and areas over and over to find better items. Also, Blizzard's parental control system doesn't apply to this. (Probably because it is an M-rated game) so you can't put hard time-limits on it.
I can see the game being very addictive for some people who just want to grind for one more piece of armor or a little more experience, so both parents and teens be warned. It also becomes very difficult to progress quickly unless you buy the Reaper of Souls expansion, which includes new items and a new game mode which really helps with expanding your character and moving up the leaderboards.
NOTE: The Real Money Auction House is indefinitely closed, so the only money-taking part of the game is the single expansion pack.