kalirion: Torchlight is a popcorn game - fun for a while, then starts getting really repetitive.

Diablo games are far better IMO, though the graphics have aged quite a lot.

At this point I'd recommend Titan Quest Gold.

Fenixp: Am I really the only person ever that strongly disliked Titan Quest and found it incredibly boring?

TCMU2009: Okay, I downloaded the Titan Quest Demo to see if I liked it, and it says it "Cant initialize graphics engine" or something like it. Does it run on Windows 7, or is the full game better optimized?

Fenixp: Am I really the only person ever that strongly disliked Titan Quest and found it incredibly boring?

Matchstickman: by the third act if you haven't built your character along very specific guidelines you're just not dealing out enough damage to kill the enemies.

FraterPerdurabo: Right TCMU2009, thanks for asking.

Basically, there's only one answer - Diablo II.
Diablo II is easily the best hack and slash ever made. The key about Diablo II is depth and replayability, this game literally will not stop. You can spend a decade fine-tuning your character (unless you're ridiculously rich). It is a game that doesn't make you feel bad about pouring hours upon hours into it. The underlying mechanics under D2 are beautiful, the game is extremely well balanced. You will start off as a scrub, struggling in the mid and late game. Once you do the mechanics, study your character, allocate your stats and skills correctly, get the correct gear, you will blaze through Hell difficulty in a full game cutting through minions like a hot knife through butter.
I've been playing this game since release and I believe the last character that I made was in summer 2008. Would probably make another one if I had more time. Also, no matter what people say - Blizzard is awesome. They released a new patch for the game a couple of years ago. Which developers still look after a 12y old game? Oh and the community is still very strong in terms of forums, fan content and active players.
One word of warning - American players are giant douchebags, though I suppose this applies to Americans in every online MP game so you might be used to it. If latency weren't an issue, I'd recommend you to play on European servers. I don't recommend playing on Asian servers, but that's for a different reason.

I played Titan's Quest for about 5-6h and while it's not a bad game, I'd still easily recommend D2 over it. Titan's Quest simply didn't feel very atmospheric to me and the skill system felt a little boring. Meh, whatever floats your boat I suppose.

Torchlight is a great game. I played through it once and had a thoroughly good time. As I started a second character, I decided it wasn't worth it. It simply doesn't have much replayability in my opinion.
Also, the issue is the endgame. Monsters respawn every time you create a new "game room" in Diablo II (your progress and character is saved, but the world is "repopulated"), which makes grinding a very easy task. On the other hand, Torchlight generates an endless dungeon with more and more levels. This means that the difficulty is more balanced since it increases at a steady rate, but boss grinding is impossible. Also, your gear will go out of date sooner. Oh and D2's difficulty isn't stagnant, you can increased / decrease it.

Diablo I suffers from the aforementioned issue. Whenever you want the world to be repopulated you effectively have to start a new game (your character is saved but progress isn't).

Honourable mention to Darkstone. That game was great back in the day, but had not aged well at all when I tried it last.

Oh and Sacred is overrated, no matter what people say. If D2's graphic style and atmosphere are not your cup of tea, maybe give it a go. But mechanically, the game feels very clumsy.

TCMU2009: Ugh, I was convinced on Titan Quest, but now I don't know. To get either Diablo 2 or TQ with the expansions would be $20 each I think, so I'll have to decide between one or the other. When you say the skills in TQ aren't as good as Diablo, do you mean the various special attacks/moves/spells you use with a cooldown timer?

TCMU2009: Ugh, I was convinced on Titan Quest, but now I don't know. To get either Diablo 2 or TQ with the expansions would be $20 each I think, so I'll have to decide between one or the other. When you say the skills in TQ aren't as good as Diablo, do you mean the various special attacks/moves/spells you use with a cooldown timer?

DarrkPhoenix: I really have to disagree with FraterPerdurabo about the skills in TQ being boring- with 9 skill trees which can then be mixed and matched for a total of 45 different classes, along with multiple ways to play each class, the skill system is just as interesting and involved as that for Diablo 2 (and I say this having spent hundreds of hours playing D2 and easily over a hundred playing TQ). Another thing to consider, that FraterPerdurabo's post reminded me of, is that something which should weigh heavily in your decision is whether you're looking for more of a single-player or a multi-player experience. While both games offer both types of play, D2 is more suited for multiplayer while TQ is more suited for single-player. A big way this comes through is equipment and drop rates- in D2 getting top equipment pretty much requires trading with other players, as the drop rates are such that outfitting even a single character with top gear would require an absolutely insane amount of grinding. The drop rates in TQ, on the other hand, are for the most part set so that you'll come across a fairly good selection of the available gear just by playing the game normally.

Ultimately, if you're looking to play with other people then D2 would probably be the better choice, while if you're looking more for a single-player experience I think TQ would give you the more enjoyable experience.

CymTyr: Diablo and Diablo 2 did not age well, D2 only has a max resolution of 800 x 600.

FraterPerdurabo: Right TCMU2009, thanks for asking.

Basically, there's only one answer - Diablo II.
Diablo II is easily the best hack and slash ever made. The key about Diablo II is depth and replayability, this game literally will not stop. You can spend a decade fine-tuning your character (unless you're ridiculously rich). It is a game that doesn't make you feel bad about pouring hours upon hours into it. The underlying mechanics under D2 are beautiful, the game is extremely well balanced. You will start off as a scrub, struggling in the mid and late game. Once you do the mechanics, study your character, allocate your stats and skills correctly, get the correct gear, you will blaze through Hell difficulty in a full game cutting through minions like a hot knife through butter.
I've been playing this game since release and I believe the last character that I made was in summer 2008. Would probably make another one if I had more time. Also, no matter what people say - Blizzard is awesome. They released a new patch for the game a couple of years ago. Which developers still look after a 12y old game? Oh and the community is still very strong in terms of forums, fan content and active players.

PMIK: Forget all the games that were mentioned before.

DIVINE DIVINITY!

Now that is the most amazing "Diablo clone" ever. It takes the diablo mechanics, makes them very challenging then adds an interesting story and character/world interaction.

Divine divinity is an action RPG that will keep throwing new things at you, and you'll never get bored till you've finished.