Most of the movies named here did at least something right.
300, childish as it may be, had great visuals
Sin City had both acting and atmosphere
Tideland, while disgusting and disturbing, was also expertly directed and had great writing
Artificial Intelligence had a gripping story and great characters. And it didn't feature aliens, those guys are really advanced androids.
They may have flaws (and some have more then others), but in my opinion they are all far from the worst. Even the spawn of the deepest dregs of pulp cinema, which is a place where I dwell quite often, is at least entertaining.
There is, however, one movie that does absolutely nothing right. That movie is Epic Movie.