Grimdango: http://www.mobygames.com/game/ultima-underworld-ii-labyrinth-of-worlds

"This sequel to Ultima Underworld plays almost exactly as the original, with its 3D world, action-oriented combat, and magic and dialogue systems. The storyline is more connected to the main Ultima series and the game world is larger and has more variety: besides the usual castles and dungeons there are such diverse locations as an ice world, a totally alien place called Talorus and the enigmatic Ethereal Void. Graphics and sound have also been improved: the size of the viewing window has been increased, there are all-new monster graphics and the game now features digitized sound effects."

mothwentbad: Can anyone do a brief rundown of what changes to expect in UU2 for those who have played UU1? (Of course, conversely for those who played just the sequel)

Lukes78: As you can read in the Mobygames summary posted above, gameplay wise there are no changes. Personally, I found the second episode a lot better because it's directly related to the "standard" Ultima storyline. It also sports a variety of environments, which make for a more immersive and diverse experience. And it's quite a hard game on the top of it: like I wrote in my general review, personally it's my favourite Ultima, together with the seventh episode (especially Serpent Isle).