If you really like the view/control mechanics of Diablo or TQ then you're most likely going to need to play Divine Divinity. It's the only one that's so focused on combat, loot, and really big areas in which to wander in the direction you prefer.
If you don't mind changing the pacing of the combat and having less to explore (but a more cohesive story in return) I can highly recommend NOX, play as the pet class (I forget the name, Ranger, Conjuror or something) but he has the most interesting and different mechanics from the tired old "Warrior/Mage/Ranged Rogue" class trio you're used to seeing.
I'd like to give an honorable mention to Gothic. First off, the controls are absolute ass and must and have designed by a drunk monkey randomly pounding a keyboard. However the game is charming, the combat is fun (even if it is more based on circle strafing than standing there and slugging it out) and the branching storylines are incredibly charming and pretty rare in video games, even today. I think you'd find yourself right at home should you love ARPGs as much as you seem to.
Now, for some non-GOG options: Crimson Alliance (XBLA exclusive, stats are entire derived from loot, and there is no XP, just Gold that you trade in for equipment), Loki (available for 5 USD on Steam, rather mediocre but randomized dungeons and all that jazz), Fable 2 and Fable 3 (though you're stuck with a lot of money earning early on in order to by your first few shops and houses), Torchlight (a bit boring after the main story but tons of mods, plus is very cheap now), and Dungeon Siege 3 (which you can get for as low as 5 USD on PC digital download if you look). I won't claim these would all "fit" but they're options that might scratch your itch depending on the particular itch. If you've played TQ/IT you've already played one of the most amazing and comprehensively big ARPGs that's come out in awhile, there's other great games, but that one's hard to match on sheer scale and completeness.
