Super Mario Bros is not a horrible movie.
I actually liked the whole "alternative universe that's populated by evolved lizards" plot line. Admittedly, it may not have been the best execution. Considering that the film is based on a game that features an Italian stereotype who kills turtles, befriends mushroom people, and smashes floating bricks with his head, it could have been worse.
Additionally, I thought Bob Hoskins and Dennis Hopper were good in their roles given what they had to work with.
What we got was a sloppy film but not entirely horrible one. I still hold the belief that, like Hook, had there been another rewrite we might have gotten something in the realms of Hellboy or Fifth Element.