It's a free game and it's supposed to be 100% free and not pay to win etc. But what I'm having trouble getting a clear answer to is: Is it an mmo? Is it full of pvp combat? They say it's like Diablo, so that means lots of pvp grief to me. Is it good enough to be worth your time? That's probably answered by something along the lines of "If you like x or y, then you'll like Path of Exile."
Thanks for any input.

Path of Exile is made by and for Diablo fans, specifically because Diablo 3 took so long. It's an MMO insofar you put up with other players in-game, but I've never had any problems with forced duels, invasions, or whatever else you're worried about. As far as I know (as a level 28 Shadow), other players are there to make any quest into co-op if you both want.

It's the deepest most complex of the ARPG games. The skill trees or pretty insane. It plays like Diablo, but Diablo is very casual by comparison. It is an MMO but you don't have to interact with anyone if you don't want to.

If you want something similar that's totally offline I recommend: https://www.gog.com/en/game/grim_dawn

It's also pretty deep and still getting updates & expansions.

I played it, but that was about a decade ago. It was back then one of the best hack'nslash games I played, basically what Diablo 3 should have been, and it wasn't like an MMO at all. I only even saw other players at some hubs I think, it played entirely like a single-player game. But what the game is like now after all that time... no idea. I have a bad feeling there's no way it's still as pure free of MMO bullshit.

If you enjoy ARPGs, you'll probably have a great time with it. I'm not particularly an ARPG fan, but I had fun... never paid for any items or buffs... and never remember seeing other players anywhere but hubs. Why did I stop? I just wasn't of the mindset to spend a lot of time experimenting with builds and skill trees.