Crackpot.756: Confession: I know quite a bit about Half-Life, but I've never played more than half an hour of it. Considering your aversion to Steam due to the whole online thing, I can't tell whether you have.
Either way, Torchlight is still fun - for a while. My mind just can't deal with the repetition and overabundance of loot, but I think that's a thing in dungeon crawlers.
tinyE: I have the original HL on disc which has none of that Steam crap. Problem is I don't know if it will run on any PC under ten years old. :P I just dug out the disc and I'm going to give it a shot tomorrow.
Mine ran just fine a few years back. Give it a shot!
That said, I too seem to only get 1/2 hour into it and then quit. :) I played the MP to pieces back in '99 or '00 (dorm's T1and LAN parties were awesome -- woot!).
As for the OP, someone mentioned Divine Divinity. I'll 2nd that one.
Also, give Path of Exile a try. I didn't get too far in it, but it was really good.
http://store.steampowered.com/app/238960/
Lastly, Neverwinter nights. There are deep RPG modules, and light hack-n-slash. That game's my baby! Luckily I found it after I was done with all my schooling. Otherwise, I'd be working at Burger King.