Oops, didn't notice it on your shelf before recommeding it.

Right, how about NOX

Awesome Action RPG, similar playstyle to Diablo & Sacred series. Noticed you have Lionheart and the other Black Isle stuff so it will probably be right up your street.

At the time of release it was very unrecognised being overshadowed by other titles. It draws you in from the very start and keeps you interested. Plenty different locations to see as you venture further out, good variety of weapons and armour as to be expected from this type of game.

Another one that is one of my all time favorites

I'd second NOX, had alot of fun on that one.

I suggest Ultima Underworld 1.
It currently costs $ 2.99, it's not on Steam, it has a wonderful story and is just a good game all around.

Third vote for Nox. I had a lot of fun with it when I picked it up months ago (and hadn't heard of it before it appeared here on GOG). Good, fun action RPG.

Chronicles of Riddick. You get Escape from Butcher Bay free & it's on sale very cheap here.

It's both on Steam and he already has it in his cart per his initial post. Great game though.

It looks like you don't have The Last Express http://www.gog.com/gamecard/last_express_the yet, that game is quite awesome. Not sure why you don't have it yet you can get it for 3 bucks right now, I recommend it, it's a gem of an adventure game. The game has different endings and it all happens in real-time so you can miss certain events in a play-through.

Nox, Etherlords/Etherlords 2, Lords of the Realm Royale Edition (yeah it's RTS, but not purely so), Arcanum (I assume you have this but just in case), Divine Divinity.