Overrated: High School Musical. A lot of my generation is very nostalgic for it, but I rewatched it yesterday and hated it. Disney TV movies are wildly overacted, and this is the finest example.
Underrated: The Platform. Its a Spanish (as in from Spain, but its also entirely in spanish) indie film about a society that allows people to serve jail sentences or debts in a special prison with an uncountable amount of floors, and food is served via a platform that takes a pile of food all the way to the bottom floors. Its a fascinating movie, and a treat if you speak spanish.