Spiritual successor to Ultima Underworld and one of the most immersive games of all time.
The first thing you'll notice about Arx is that the interface takes a little getting used to. In the first review I ever read (before I'd actually played the game), throughout the entire game, this particular reviewer somehow failed to discover that you can close the inventory bar by right-clicking anywhere on the screen, and he gave the game a poor review on accounts of its purportedly terrible control. If you're not retarded, you should have very few problems with it.
The magic system in particular is what sets the interface apart from other games, and although that isn't what drew me into Arx, it is worth an honorable mention. While holding down the spell key, you "draw" spell runes using the mouse cursor. Spells have a minimum of two runes. When you've drawn enough runes to complete a spell, it is immediately cast, or you can store it for later use (through one of three hotkeys). This system feels rather ingenious at first, but you'll quickly become frustrated with it when you try to cast spells during combat. The ability to hotkey more spells (say, up to ten? there are ten number keys after all) would have been not only welcome but sensible. Nevertheless, Arx's rune system speaks for the game's interactivity.
And that is probably my only real complaint about Arx Fatalis.
The second thing you'll notice is how unbelievably immersive the game world is, from the gorgeous textures and creepy lighting to the amazing environmental audio. There are parts of Arx Fatalis that absolutely astounded me on my first run through the game — I don't want to spoil anything, but wait until you see the Temple of Akbaa. Atmosphere is probably Arx's number-one selling point, putting it in the same sensual vein as Clive Barker's Undying.
The story is also quite fascinating. Again, I don't want to spoil it for you, but you'll be amazed when you play the game two or three times and discover that you can finish it pretty much however you want. Whether you play the hero and save the people of Arx, or become the villain and kill everything in sight, you'll never be stuck without a key. What's even more remarkable, despite that there's only one ending, it actually makes sense whether you're the good guy or the bad guy. My advice: play the good guy first so you can see the whole story and meet all the characters. Next time, go ahead and give your sword arm some exercise.
(Very minor spoiler in the next paragraph.)
I approach Arx's level of Interactivity with some equanimity. On the one hand, you can do more in Arx than you can in most games of its kind. One of my favorite past-times is baking apple pies in the goblin kitchen, where you have a stove and plenty of ingredients. Unfortunately, apple pies are the only thing you can bake, wherein comes the other hand: there's not nearly enough interactivity as this game honestly deserves. Some more recipes would have been wonderful, as well as some new weapon models to forge in the dwarven mines. I feel like Arx just doesn't have quite enough. Enough of what? Everything really, but it was a very admirable attempt, and far beyond what most developers have accomplished.
If you're an RPG or adventure fan, you must give Arx a shot. The engine is dated, but the graphics and sound still hold up. When you go to the bargain bin looking for your next time sink, and you see Outcast and Arx Fatalis sitting side by side, pick up Outcast . . . but if you've already finished Outcast, then it's time to give Arx a go.