I'd call the community a mixed bag, based on experiences with StarCraft, Diablo 2, StarCraft 2, Diablo 3, and World of WarCraft.
There's a lot of genuinely kind and helpful people. I've met a bunch of people that these days I consider good friends, even outside of the games. I also find that people are usually willing to help out.
That said, the games do have their fair share of trolls (see: WoW trade channel) and elitist pricks who won't even give you the time of day if you're a "filthy casual"/missing a certain achievement/not suitable geared to their liking/etc. In my experience though it's generally their forums that are more toxic than the games themselves.
On the upside, I haven't seen much of the impatience that everyone often cites. I hear all the time about players getting fed up with a party and bailing at the first wipe or if things are going too slow for their liking, yet I rarely ever actually see that. I've also played healers as my main characters ever since vanilla WoW, and I've never personally been a target of the commonly-mentioned healer abuse whenever things go south. That's even including pick-up-groups.