I really liked Arx, as well.
One thing I think thing the game had a hell of a lot of atmosphere, to say the least. Arx is underrated and I do need to finish it.
One thing about Arkane Studios -- all their games, out-the-box, seem to be buggy. See Arx and Dark Messiah, out-the-box. Though, after a few patches, those games were the way they should've been straight-out-the-box. I hope they can change that, for future games -- getting them for the most part running fine and not-so-buggy, right-out-the-box.