I own this game on steam and used to play it back when it released (came out of early access). I remember it having no UI for controller interaction and it was somehow weird to play (pressing "d-pad up" for interaction and so on). I played a while but then switched to another game. I tried to come back a few times but never really felt at home with the controller in this game. I think that a UI showing buttons for interaction would help a lot and so I was thinking "why not just ask here?".
I would totally buy the game again if it had "proper" controller support, since I stopped buying steam games and am currently trying to move to GOG. I have two (PC) systems on which I play (both connected to a TV, so I am playing from the couch using a controller) and I am trying to find something to play on GOG, but my criteria are "controller support" and "cloud saves" (so I dont have to manually drag the saves around everytime I play on a different system) and since Grim Dawn seems to be the only game (almost) fulfilling these criteria (that I havent played through yet), I would be very happy if I got a second chance with it ;)

The game is based on TitanQuest old engine, so it's starting bad for you..

I dont think it has anything to with the engine, it is a simple UI change. If "enable controller" is checked, use UI xy.
The "only" thing that needs to be done is to place the button-icons over the corresponding boxes and fields.

??? I never knew this supported a controller at all.

Well, now you know and can find out if it suits you :)