Even though I'm a hardcore
Nox fan and personally think it's way more than a Diablo-clone that was unfortunate enough to be released at about the same time as Diablo II and, thus, being the less popular of the two, automatically being called a Diablo-clone when it's definitely not, my recommendation still stands. Go get this game. Sure, it hasn't got procedurally generated levels and mobs don't respawn, but it has quite an innovative system -- for its time, mind you -- and offers you non-stop fast-paced aRPG action requiring some skill management and fast reflexes, all the while giving you some environmental puzzles and a few NPC sidequests. The levels are brilliantly designed and you'll find it's a game that aged quite well. Plus, there are some online modes that are sure to make you keep coming back to the game as soon as you've finished all three main campaign quests (Warrior, Wizard, Conjurer). Nox is a somewhat dark game, though it never looses touch with its particular kind of humor, which you will find all throughout the different campaigns.
I kind of recommend
Torchlight, even though it's a bit more light-hearted than the Diablo games. As has been said before, some of the old developers worked on it and it has tight gameplay, albeit in a more "cartoony" world and taking place in pre-designed levels. It's enough to scratch that Diablo itch for some time, but it definitely won't replace the originals for long, as it gets tedious and repetitive fast enough.
I can't, for the life of me, recommend
Divine Divinity. Probably my biggest dissappointment here on GOG, along with
Outcast. Fans of the game praise its humor, but as far as I'm concerned, I didn't find it funny in the least. The game is slow as hell and is more in tune with the Infinity Engine D&D games than with Diablo. The story is not engaging, the game definitely didn't age all that well, combat is frustrating and tedious, "unless you know what you're doing" -- which is to say, far from being entertaining and fun, just your regular "strategize everything and run away a lot" -- and it takes A WHOLE LOT OF TIME to start. Seriously. I've never even left the starting town, and the only time I was about to, after 5 hours or so, the game crashed on me and I said "screw this". So, for old Diableros, trust me: Divine Divinity is a big no-no.
I'd stick with Nox and Torchlight.