The Dark Side’s more fun in KotOR II, because your companions start feeling it, too. And some of them you can convert to being a Jedi. Or a Dark Jedi.
This site compiled all the known missing content. It’s not very well organized, and a lot of the information is repeated several times, probably due to the multiple paths that the player can take, but it’s all there.
These guys are working to restore the lost material back into the PC version of the game (with potential for an Xbox mod in the future as well), adding new models, animation, and cutscenes to fill in where Obsidian left off.