Arx Fatalis, the greatest game since Ultima Underworld

You can get it very cheaply from Good Old Games.
Ok, what is so great about it? I will give a few hints and let you discover the rest for yourselves:
- you make magic by mouse gestures (you move the mouse in certain patterns, like in Black and White)
- the AI characters yell for help from associated NPCs and run away when too hurt
- I once ran into an impenetrable beast that could kill me with one touch. Running away from it I reached a dead end. I expected to find no way out, but the beast disappeared and reappeared a few feet behind, just enough to let me run away.
- I couldn't find ONE spot where I would have gotten stuck in the entire game.
- the quests are intelligent. You need to use brains to finish this one. It's not something that must be searched on google to finish, either. If you have the will, there is a way.
- you can kill almost every character in the game as well as finish their quests.
- a lot of side quests. You can finish the game in a week or in a few months, it depends on you.
- hidden magic spells. Each rune has a specific meaning. Try combining them in innovative ways.
Update: I have found a Doom3 mod that tries to be a prequel to Arx Fatalis. A pretty neat effort and I am glad I found a new reason to upgrade my computer :). This is their site: Arx – End Of Sun and this is a gameplay video: Arx - End of Sun (Gameplay Video #1) [Doom 3 SP Mod].