For me, they showed how a city could be just as fantastical and action-packed as a dragon's den or elvish forest. That a city is a character all on its own. And also driving Thieves World were the characters. They were complex and not always heroes. I think we all developed our favorites, and it was always a treat when they'd show up.
While the movie itself still stands as one of the better fantasy films of the 1980's, the soundtrack, however, has not aged particularly well. It really should have had a more classical sound to it rather than the '80's synthesizer stuff they went with.