Ultima Underworld 3
With the recent bargain prices on old Xbox games now that the 360 is out, I picked this up for like $15 and it was worth every penny. I must have sunk over 40+ hours playing through this game from start to finish, and I didn't even do every side-quest.
There is not one element that is outstanding here, but the sum of all the parts is really what makes the game great. I really had a good time wandering around the 8 levels of this dungeon crawler and was really satisfied with the games length. In fact it ended just as soon as it started to feel a little too long.
I did have a few crashes on my machine, that were not too troublesome and were solved by the old trick of loading 3 other Xbox games to clear out the cache and force it to re-load from the DVD.
In summary, it's a little outdated, but still very enjoyable, and worth trying out if you are interested.