4. Sam Witwicky - Transformers
Why's he hated? Transformers is about giant metal robots fighting each other. Sam Witwicky is not a giant metal robot. Fans don't like this. Unfortunately, Michael Bay insisted on having him as a constant factor in the films, even being present during major battles where he only serves as a distraction. On top of that, Shia LaBeouf has acquired such a hatedom with regards to his other films (especially Indiana Jones and the Crystal Skull) that a lot of fans just dislike him by default.
Why's he underrated? If you're one of those fans who thinks that the Transformers franchise was perverted by Michael Bay, I've got something to tell you: you're stupid. I mean it... you're freaking dumb. The entire point of Transformers was to shill toys to kids. There isn't any depth to work with. The only adaptable themes from the series are "humans are worth defending" and "giant robots are cool." Witwicky serves both roles. The robots aren't impressive to each other, so we need a constant human perspective to maintain their awe-inspiring nature. Sam Witwicky, weak little chump that he is, is the most "human" human being in the cast. His willingness to jump into the heat of battle, despite his obvious shortcomings, also justifies Optimus' belief in the strength of humankind. Now stop being stupid, fanboys.