Challenging and highly atmospheric, if also heavily flawed, dungeon crawler/immersive sim that is in many ways highly reminiscent of Looking Glass Studios classics. You'll journey trough decaying underground world filled with dark ritual, bloodthirsty enemies and eldritch horrors.
Patience, experimentation and careful exploration are often rewarded, and also quite often -required- in a way that is rarely seen in modern games: Arx offers little to no hand holding to players during their journey through its sprawling, interconnected dungeons - thorough exploration and paying attention to clues and readables are keys to making any sort of progress!
Game isn't without flaws tho: magic system, while original and also quite impressive in a sheer number of offered spells and their possible effects, is also somewhat clunky, and spellcasting is often unresponsive. Controls & interface in general will take some time to get used to.
While game offers to player a freedom to develop his character in many possible directions, some skills are definitely far more useful than others, and some playstyles are far less developed than others. Stealth system for example is quite unrefined, and while it is sometimes useful and at some points borderline required to sneak (say early encounters with dreaded Ylside warriors), stealth tends to be rather useless and unsatisfying.
There is quite a bit of different types of fun-to-use melee weapons, each with their own pros and cons. Ranged combat on the other hand, while quite useful at times, is made unnecessarily monotonous by the fact that the player is offered all of -two- bows, second one being pretty much unreachable on first playthrough without any outside help.
Still, I'd say this game's assorted shortcomings are -very much- worth dealing with, and are far, FAR outweighed by its many qualities.
Pretty much recommended to anyone with some patience and willingness to deal with game's flaws and idiosyncrasies.
Also, i highly recommend using Arx Libertatis: it offers additional bug fixes and eliminates issues with modern hardware.