Well, not exactly bad, lots of people seemed to like them, a lot. I can understand that, I just don't agree. It's true that each had redeeming qualities, but not enough to overcome their essential off-ness:
Superman Returns, Bryan Singer's love letter to the Man of Steel. Unfortunately, Singer missed the whole point of Superman being, you know, super, and was both cavalier about the perils of kryptonite and widely off-the-mark in his characterization of everyone, including Perry White, but perhaps most egregiously Lois Lane. You can't re-write the canon, Bryan. It doesn't work that way.
Miami Vice: all atmosphere, no story. Looks great, less filling... OK, I'll stop, the same way I stopped watching the movie about half-way through. B-o-r-i-n-g.
Come to think of it, Superman Returns was also boring. There's no reason at all for these movies to be as long as they were with the amount of story they had to tell, and especially the small number of characters they needed to portray. They were both extremely flabby.
Flab's bad enough around my hips, but it's inexcusable in a film. Oh, for an editor who's not in love with the long, long, long shot!