RPG Games like Diablo or Path of Exile

Titan quest

But diablo 3 is best

Those games are not RPG just H&S...

Sacred 1/2?

Fate. Some people are put off by it's art choices though.

Dungeon Siege series?

Sacred series, Van Helsing

Nox by Westwood, i believe you can get it on gog.com, it's old though so you may not like it

If you want a cheapie, there's space hack, but yeah... sounds like you've already went through the best. already.

CSGO

Grim Dawn but actually is in early access and i read that there are not legendaries (they will be added in near future)

borderlands 2

I honestly played only Diablo 1/2 (+LoD), Torchlight and Path of Exile, liked them all even if I don't consider myself a fan of the genre

Try Divine Divinity - it was an attempt to make more of an actual RPG with Diablo-like battle system.

if you have any interest in the Marvel universe Marvel Heroes is a fine ARPG

Throne of Darkness was so awesome back in the day. I think you can find it on GOG. There was also Harbinger if you want a sci-fi H&S and you don't mind older games.

My friend said that Divinity Original Sin is good :)

What about the Deathspank games? They're rather silly, but are the type of game you're looking for mechanic-wise.

Inb4 someone says "Baldurs Gate".

Good but old: Dungeon Siege 1

Not so good: Loki, , Legend: Hand of God

Parody: DeathSpank

On the other hand - Darksiders 2?

Titan Quest

You have pretty much played all the best "Hack & Slash" games you'll find on the PC unless you are looking to play older games, many which were mentioned above. If you have access to the PS2, there are a couple good series to check out, such as the Champions of Norrath series, the Bauldur's Gate: Dark Alliance series (VERY different then the PC RPG series), and the X-Men: Legends series.

A few good PC games though that come to mind.

• Dungeon Defenders - The game is ALL about finding great new gear, which can be leveled up to make it even stronger. However, it's not your typical Hack & Slash game, since it's mostly mission based as well as half Hack & Slash and half Tower Defense. The game is a blast though if you have others to play the game with.
• The Mighty Quest for Epic Loot - Another "Free to Play" game that focuses around you finding "epic loot" as said in the game's title. However, it's also not a typical "Hack & Slash" game, since it plays out against other players as well as being half Hack & Slash and half a "Dungeon Keeper" sim (Build your castle, place traps and monsters to defend it). You either defend your castle from invaders or loot other player's castles.
• Marvel Heroes - A mostly free MMOARPG that will have you running around as Marvel Superheroes, fighting baddies and collecting new gear along the way. I personally never could get into it, but I know plenty who have. If you want to play some of the AAA list heroes though, you can expect to shell out some cash.
• Marvel: Ultimate Alliance series - Plays out very much like Marvel Heroes, but it's not an MMO. Tons of heroes to choice from, level up, get better and better gear. They play out very much like your typical Hack & Slash game.

Also, checking around online, a few free to play MMOs popped up that claim to play like Path of Exile and Diablo, such as Akaneiro: Demon Hunters, KingsRoad, and Drakensang Online, though I have never played any of those personally.

Hope you find something good to hold you over for a while! Great Hack & Slash games are few and far between!

I know its not really similiar, but pretty much anything I could think of was already posted, have you played Alien Swarm?
It has quite nice progression, classes, and killing tons of stuff. Another thing might be Gauntlet (havent played so no idea how it is) and Hammerwatch.