I put some more time into this yesterday and today and made it into Act 2. Toward the beginning of that act, the game seemed to switch to some kind of turbo-XP mode, where every five or so kills would give me a level. Maybe just a way to make sure you're ready to take on the quests there (and I probably wouldn't have been, coming in it at level 25 or so for a bunch of 32-40+ quests), but it was surprising.
My character's a warlord, now with berserker as his hero class, which is fairly cool. Favorite abilities are leap attack for a quick close-the-gap stun, and the area of effect stun if there's too much to handle. I've been loading up on equipment that adds to damage above all else, and that makes up a big part of my DPS, with a couple pieces of armor having stats like "adds 20-220 arcane damage." I'm dual wielding, as that seems to gain double the benefit from such equipment on regular swings, although the special attacks hit for less than they would with a big two-hander.
Earlier in the game, around level twelve or so, I was having a rough time with some of the quests, having to hack at monsters for what seemed like forever while they took off a good chunk of my life with each of their swipes. I think I was under-leveled a little then, but I came across some gloves and a hat that added quite a bit of damage and started having a much easier time.
I've run across a bug a few times where an enemy, generally stuck on a corner or something, becomes untargettable and invincible until he gets unstuck. The follower AI is pretty terrible, the mage follower wasting mana casting fireballs at walls, the healer preferring to cast offensive spells instead of her heal when I'm getting a beatdown, the fighter charging off to engage a totally different group of monsters when I'm in the thick of others. Mine die a lot, and I've mostly given up resurrecting them on the spot, just switching to a new one until I portal back to res them all at the healer.
Definitely lacking polish, but still as good a cop of Diablo as I've played in a while. The loot system in particular is wayyyyyy better than that in the Untold Legends games, which is really what keeps these games going for me.