I was hesitant to install and play the demo, but I figured that after downloading 500+ MB I owed it to the internets to not have wasted all that precious bandwidth. And then I got stuck for about 24 hours. It was frustrating at the beginning, because the game 'crashed' twice in the tutorial (some graphics issue froze the game with only momentary stutters of mouse activity, happened on some isle while I had the book open to figure out how to use Dark Path, happened one time again later, also while having the book open). And it kept being frustrating while I learned how to dodge the academy students who were set to hunt me (with spells!) while I hunted coyotes (the evil starting quest). Died a couple of times until I (by mistake) cleared the entire area with no intereference from the pesky students. Because in my frustration I had forgotten to talk to Magnus to reactivate the quest. But that meant that I was level 3 when I finally did that quest, after which all enemies outside the academy vanished. No more respawnings there.
And that's close to what I've found outside Avon and the Miner's Village as well. Outside Avon I can get a few enemies to spawn by reactivating the coyote quest, or maybe that only spawns coyotes and the other enemies are respawned naturally? Still rather slow respawns though, and apart from the goblin quest in Miner's Village, I haven't seen a single enemy respawn there, or in the Northern Outlands, or in the Northeastern Outlands. No spawning of enemies behind my back either, though I probably wouldn't notice anyway, because I often don't know where I am.
All in all I think that the 'big picture' is a huge improvement over Diablo 2, but the actual playing suffers from too many flashy effects. A lot of spells seem to take some time to cast, but that isn't shown as an animation, it's shown as a timer on the mouse pointer. Like realtime with pause - I get to move around for a while, but not cast a spell until it's 'my turn' again. That's pretty crappy, especially combined with the targetting difficulty and the lack of click-and-hold.
I began to use an undead minion just so I wouldn't have to bother keeping track of every little enemy, and later on I began the practice of summoning both a demon and a champion to help out with that. It still seems as if all the spells arent properly balanced, and especially most curses seem weak in comparison to direct damage spells. With my limited multitasking/multithreading/manual dexterity, if a combat spell isn't among the 8 best, then I don't have any use for it. Though I suppose that a lot of spells are really meant to not be raised beyond the necessary initial spell point, but rather used while wearing a crapload of items, all carrying one or more of a rune with "spell +1". Well, maybe, or maybe not. Maybe a bunch of identical rune effects don't stack.