Hi Wawa!
Not many people are frequenting the forums, well, not at this moment....I will give you my quick overview and if\when I have time I will add some meaningful things up!
So, here we go:
Firstly, give a nice view to a Seth fellow if you hadn't already
https://www.youtube.com/watch?v=SgAn68Uy2jQHe made a nice and quirky review but it's mostly to get you into the mood.
Also you can check underrail wiki if you want to check some simple elements of the mechanics (also armors, weapons, etc.)
Beware, just don't go too deep, you don't need to be a wiki junkie. Better to dive into a game and just play!
My take? Where to begin...
You have 23 skills governed by 7 base abilities. Game is mostly combat and exploration based but there is a plenty of opportunities for you to outrun or sneak out\sneak around (some silver tongue and slyness here and there). In some situations even with some repercussions...
No companions though but you will work side by side with some NPCs during a certain situation or two.
There are many mechanics that you will learn during the course of the game, some of them are rather obscured but that adds the flavor in my opinion. Many, many cool weapons and armors but for those I would need more time to explain...
Eh, that is all for now. Sorry! When I have the time I will tell you more.