I've been playing Car Arcanum a lot, and it is really good fun. There is much new stuff, some terrifically difficult battles, new locations, new puzzles, new followers, new thief quests... Even wilderness traders are more interesting. Each game you play can be particularly different because you can choose really different flavors of sidequests, and get even deeper into types of roles. In addition, there is no spoiler walkthrough for Car Arcanum. if I get lazy about a challenge, I can't just pick up a wlakthrough and read what to do. I'm on my own. (In one new place in car Arcanum, you come upon a strange statue/altar. An inscription advises: If you were only smarter, you might understand...)
