I haven't seen many but the weakest of what I saw was definitely Hulk. There were some pretty good parts, but they were unfortunately surrounded by a bunch of boring scenes. I loved the transformations and some action scenes, but those were pretty much the only good parts. Plus, the ending is kind of confusing and uneventful. It's just too long, too boring and tried too hard.
Luckily, they stepped it up with The Incredible Hulk.
This movie was cute, from what I remember. But I wouldn't count it as a superhero movie... or at least a legit one. 
and Man of Steel (boring as hell 