RPG Games like Diablo or Path of Exile

Van Helsing and Torchlight 2

Bastion?

Try FATE! It´s simple, but you will enjoy it!

Drakensang (Online)
The Mighty Quest For Epic Loot
Marvel Heroes
Hammerwatch
Kings Road
City of Steam
Realm of the Mad God
Din's Curse
Evoland
DarkEden

EDIT Arcanum: Of Steamworks & Magick Obscura FallOut 1+2 The Temple of Elemental Evil

the newest divinity is pretty damn good.

Just because no-one has mentioned it, whether it's relevant or not...

Nier.

Try Gauntlet

Divinity 2, Director's cut. That's an action RPG with loot and such.

Silverfall.

Neverwinter Nights and Darkstone. Both are old, but gold (Or so I've been told).

Torchlight 1 & 2

If nobody mentioned them yet, Grim Dawn and Divinity: Original Sins are both great games from what I've seen/heard.

Here's one I'm surprised noone mentioned. You could try Marvel Heroes. It's a MMO just like Path of Exile.

I had a huge post typed up but I changed my mind. Instead I'm going to link you to a video from a guy that looks at and gives honest reviews of MMO's. The video is only a couple weeks old, so it's still relevant. I put a lot of my personal faith in what he says.

MMO Grinder: Marvel Heroes