Ok. So let's say (hypothetically) that you were an early-30s female who has never played an MMO-type game before or any kind of game with voice chat but were generally pretty handy with a Doom shotgun. Hypothetically, if I go online and play this thing with a headset in, is it going to be full of squeaky-voiced pseudo-anarchic teenage sexist homophobic fake-meatheads ruining my one night with the flat to myself? Hypothetically. (Obviously, this is hypothetical. Hypothetically.)
Played with a woman in my party the other night for a few rounds and never heard anyone say anything about it. She also basically had her baby on mic (I'm assuming the relationship based on the conversation; I don't really know for sure), and after saying, "Can you sound like a monkey?" and the following child-monkey sounds about 30 times, I was surprised no one said anything about that either. It was a humorous and refreshingly different online interaction.
But of course, there are only ever four people in a room at a time, so this single example doesn't mean a whole lot. I would like to think you could enjoy yourself without any kind of harassment, but sadly there's no way to know for sure.
As for the mechanics, with the exception of the melee combat which takes a bit of practice, the shooting is pretty self explanatory and that's about 80% of the game. There are also some infrequent platforming elements (wall-running) that are absolutely not self explanatory, so you might want to watch an intro video online or something. The MMO element is largely irrelevant unless you want to get super deep into the game and get involved with clans (I don't know that I ever will, but I'm still enjoying it).