I kinda explained it in my first post... I noted that pretty much everything has improved, I just didn't like it as much. It wasn't 'new' to me anymore, and therefore lacked the magic that the first one had, cause at the time that I played DF, I'd never played anything like it before. It just felt like more of the same.
If I was reviewing the games, I would definitely rate UC2 higher than DF, as all technical aspects are better (graphics, music, sound, AI, etc.). But if I had to choose one single player campaign as my favorite, I'd probably pick DF.