Diablo was a groundbreaking, fantastic experience at the time.
The dungeon music, the slowly revealed dark areas, the shrieks, the sounds, the epic items you could find...
It was amazing, and gamers were blown away.
We were.
Diablo II lost much of that atmosphere (almost all of it).
And I agree that the respawning areas killed its soul, turning the game into something players felt GUILTY about playing (which is an interesting psychological phenomenon since, at the end of the day, every game has you "wasting" time by clicking and typing stuff in front of a monitor anyway).
Gems and set items were a cool addition, but there was NO way in hell to acquire a full set in single player, not unless you were ready to grind for EONS. Which you started doing, until it all felt stupid, pointless and depressing.
Still, when at their best, these games aren't even as mindless as they are commonly depicted. They can be quite difficult, and you have to give some thought to your character's progression if you want to stand a chance in the later stages.
I'm playing Torchlight 2 right now, and overall I like it.
The ease-of-use additions to the formula are a godsend, and in this game it IS POSSIBLE to complete a set of armor. I just did, in my first playthrough.
Also I've just discovered the joys of hot-keys remapping, meaning that I've become able to mix more skills more effectively, for a frantic, more satisfying experience.
So, in the end: there's fun to be found in this genre, but you have to stay lucid, play straight and true and cut it when it's time.
If they dared to remove the sick respawning mechanic (while implementing a less randomized itemization), half the problems of all these Diablo clones would be solved since - well - they'd become more like Diablo again.
P.S.:
I've not even considered the existence of Diablo 3 because, well, Always-Online requirement and, excuse me, Auction House?
What am I, a self-aware junkie?