A conversation started about wretchedly bad films in the Fallout 3 thread, and I thought I'd comment here as it is closed.
I agree on Waterworld. It was so bad it actually ruined The Postman's chances of success, which is a film I thought was pretty good. He spent a ton of money on an epic, and it was just super meh.
I don't really get the 300 hate though, I thought it was a very fun stylized action movie. The over the top visuals and buckets of blood made it feel like a video game, and I thought it succeeded at what it wanted to be.
Transformers 1 = Good.
Transformers 2 = Bad.
But seriously, like GI Joe, any movie based on a toy line is aiming pretty low in terms of artistic merit, and so I never go in expecting an epic, so I wouldn't throw the wretchedly bad sticker on them.