The title says it all, really.

My THQ Nordic favorites so far? Impossible Creatures and Neighbours From Hell.

Gothic II

Titan Quest.

Though when I bought it again when it became DRM free by coming to GOG, I found out this second time I couldn't play it as playing the game gave me the first signs of RSI and I quit. I don't know if I clicked in a different way the first time around, but it doesn't help that even though you can repeatedly attack by holding the left-mouse button, I automatically click for every swing I want to make.

Hmm...nvm. I guess I'd go with Gothic, though Titan Quest is the one I played the most.

Newer ones:
The Dwarves - high-res choose-your-own-adventure game with some combat thrown in.
The Book of Unwritten Tales 1 - fun, albeit somewhat telegraphed, comedy point-and-click. (The sequels suck.)

Classics:
The Nations series - a humorous and upbeat 4X (the last two Xs stand for exhort and exhilarate).

The first Red Faction.

Titan Quest. I'm a sucker for Diablo clones. :p

Painkiller: Black Edition (it's actually two games in one package). But I don't consider them to be THQ Nordic games since that is not the original publisher and THQ had nothing to do with making those games.

There's a lot of good stuff to choose from, but I have to be boring and just agree with everybody else that said Titan Quest

The Raven: Legacy of a Master Thief because it is a good point and click adventure.

I'd have to go with this as well. For the time being only though, as there are a number of THQ Nordic games in the backlog that I've not yet played.

Technically, NEXUS: The Jupiter Incident is now a THQ Nordic game. It gets my vote.

Supreme Commander: Forged Alliance

Maybe Darksiders & Ori and the Blind Forest? Although I have to admit, I've never actually finished them ...