Here's something that bothers me about the graphics debate. There is a difference between bad graphics and bad art style.
I don't expect high-tech graphics, but you can make something that's at least pleasant to look at, even with low tech. If I am going to spend many hours playing something, I don't want to hate looking at it. I can handle low res graphics that have some style; I might even like them, but take horrible art style and blow it up into HD... and its still horrible.
Calling Underworld's style horrible might be a bit too harsh, but it certainly is ugly. It looks as though "Poser" characters were used, which is a dead giveaway that someone who cares nothing about art was in charge of the art. The "hodge-podge" of styles that others mentioned is also very visible.
My complaints about the style should not be very insulting, because frankly, I doubt much thought was put into it anyway. If it is made by a 1-man team, then I guess its understandable since he's probably a programmer and not an artist. But I'd even rather see poorly drawn sketches than generic Poser models. I don't want to discourage the creator, or anyone else looking to make old-school games, but encourage them to at least put a little effort into how the game looks regardless of whether the graphics are "fancy" or not.
All that being said, I will probably still buy the game, because I really love the old Wizardry style of game and support them any chance I get.