Another genre I was vaguely aware of existing, but didn't have the name for. Apparently, things like Diablo 3 (pretty much the only other example I'm really aware of, so poor show me) are called action RPGs, or ARPGs. As far as I can tell, the difference between ARPGs and what I would typically compare it to, such as Fallout 1+2 is that this doesn't have a turn-based or pause-to-command system. Instead, everything you do, from swinging swords to casting spells is in real time, and so is generally a lot more frantic.
Luckily, what isn't frantic is the upgrade/class system. You've got six classes to choose from. Each of which has a skill tree, only part of which you're likely to unlock over the course of a game, being limited by a max level (though I've no idea what the level cap is. It's possible there isn't actually one, and you could just keep grinding to fill the skill tree. I've decided it's more fun to find out by doing than by reading about it.) This skill tree is complemented by abilities you can buy with "Devotion", effectively a measure of how well you explore the world.
The end result of this is that there's probably thousands (or more) possible builds. (Just to demonstrate the complexity, there's actually a web-based system for you to play about with different builds here. You can really muck about and try a range of different playstyles, including ranged, close-combat, summoning and more. This also means you can make yourself an utterly useless character very easily. My first character was a jack of all trades, master of none sort. He tended to die when stabbed, wasn't very good at using magic and had a really weak sword arm. I'm having much more success with my second character, the thematically purer "woman who likes to shoot things in the face". If you're anything like me, you'll be measuring your success in deaths.
Gameplay is repetitive, in that you're going to spend most of your time finding things and then killing them. There are bits and pieces of quest structure here, but the quests mostly involve finding things and either killing them or bringing bits back after you've killed them. Still, that doesn't seem to actually matter. At this point, I've put about three solid days (not all at once, though it's close) into finding things and killing them, and I feel that urge to get back onto the computer and do it some more. That's quite a good sign.
There's also masses of items. You'll find yourself attempting to collect the various sets, especially given the fun additional skills they can provide you. Currently, I shoot fire, lighting, explosions and some sort of poison, which I don't quite understand the source of. I am a sexy shoeless god of war. (Though I am wearing shoes. They give me a plus two to defenestration.)
All the mad fun of an FPS, but with the complexity you'd expect in a fairly deep RPG.