Arx Fatalis is a good RPG that's got some interesting twists to it but an overall experience that's a bit hollow.
Like any RPG, Arx Fatalis has a pretty reasonable and developed skill system. Your character has four primary attributes and sixteen different skills to which you can assign points as you level up throughout the game.
The spell system is one of the most unique systems you'll find in any RPG.
As you progress through the game, you will acquire up to 20 different runes. There are 40 different spells you can cast, each which is cast by drawing the appropriate runes that make up the spell. Instead of clicking a picture in a book or just casting a spell with the touch of your mouse, to cast a spell, you have to draw out a series of runes on the screen. Because this can be rather difficult to do in the heat of battle, you can pre-cast up to three spells that can be cast in an instant when necessary. For the most part, this works just fine, but if you find yourself up against an enemy or two that requires more than three spells, you're going to have a very tough time getting those extra spells cast while under attack.
Arx Fatalis also has a fairly detailed object system where you can combine many different objects you find in fairly interesting ways. For example, you can add water to flour to make dough. Dough can be cooked in a fire to make bread or rolled into a pie with a rolling pin. Add some apple and you can bake an apple pie. Apply some rope to a pole and you've got a fishing pole. Crush up some flowers and you can make potions.
In spite of the decent number of spells and very interesting combinations of things, the overall sense I got from Arx Fatalis is that the complexity of these things exceed the rest of the game. Most of the spells you can cast are never necessary and you can get through the game using just a couple of them. There are a great deal of alchemical ingredients, potions and foods throughout the game but I almost never needed any of them throughout the game. It's cool you can bake an apple pie but if you've never got a need for an apple pie, it becomes merely a novel thing to do.
The game also has a bit of a sparse feeling to it. There are very few monsters to kill in the game, not many NPCs to interact with and not many settlements to hang around. There are not that many steps to the main quests and there are only a small number of side quests. The only thing that prevents this game from going by very quickly is that it takes time to figure out what to do next or to find the solution to a problem facing you.
Completing quests in the game can sometimes be a frustrating experience. You are often asked to go find something and given absolutely no information on where to look. You will find yourself wandering the levels from top to bottom until you come across that passage that was previously blocked, find that right person to talk to, or meet that person who wasn't there before. I don't like RPGs that do too much hand-holding but I think Arx Fatalis could be a little more helpful.
You will also encounter a number of puzzles throughout the game that will require the subtle observation and keen thought that you often have to put to use in a good adventure game. If you've got the mind and patience for these challenges, you will enjoy them. Otherwise, you'll be frustrated in playing an RPG that routinely gets you stuck on how to proceed.
While your skills do improve over the course of the game, I must say that I didn't really feel much of proper character development. I played as a magic user and each time I leveled up, I can't say I felt any different. Early in the game, I picked up the usage of my fireball spell and stuck with it to the end of the game. Almost all of the monsters in the game could be taken out with one or two fireballs so there wasn't much of a need to use other spells and increasing levels never had a noticeable impact on the game play although I'm sure I would have noticed a change in difficulty if I didn't level up.
There's also no sense of progression in learning spells. As soon as you find the proper runes, you can immediately cast any spells for which you've got all the proper runes. This means that very early in the game, you'll be able to cast very high level spells. As you gain more runes (and you can get a good number of them fairly quickly), you learn more spells but not necessarily more powerful spells.
One element you find in almost every RPG that's completely missing here is that you never have any options in dialog. When you interact with another character, your character speaks a pre-defined script without giving you any decisions in the matter.
A final element I just have to note is that the voice acting for the main character is just wrong. The actor decided to go with an arrogant and constantly condescending tone that is completely out of place.
This game is definitely worth a play by someone looking for an RPG to play but it's far from a grand and outstanding experience.