I hope the atmosphere will be as great as U1's. There are SP games that have better (and especially more original) gameplay and a better story IMO, but it was just great to visit this planet with its valleys, villages, castles and temples. Somehow it gave you the impression of a "real", existing world. You didn't run through some nameless corridors or facilities, you travelled through Bluff Eversmoking or the Sunspire; you didn't visit some dubious Alien world with stupid caves with Aliens that hide in corners but you got to know places like Na Pali Haven where you could imagine what kind of culture could exist there. At least, that was what I liked most about U1.
Of course, U2 doesn't have to copy all this (and it won't do that - you aren't alone any more or trying to escape from a planet), but I hope it will provide a great feeling while you play it, not just some stupid "I am a highly skilled warrior trained to kill nasty aliens that run around some stupid planet and kill human beings"-game. If you look at the Screenshots, the engine should be able to give us some great SP experience (hmm, OK, we all knew that); also it is said that we'll be able to visit many different locations, there will be different Skaarj clans and stuff like that, and also - it's developed by Legend, and I liked WoT for similar reasons.
So, what I wanted to say is: I hope U2 will be a "soulful" SP game.