Inspired by the linked XKCD. Using 60% instead of 50% because that's an easy filter to apply on rottentomatoes.
I'll go first: I think "Sherlock Holmes: A game of Shadows" was awesome, from the plot to the characters ,and especially how they used screen-play to highlight how Sherlocks head works in these absurd ways.
A much harder stipulation is that it needs to be below a 60% audience score, too. I haven't found any there, yet, but it feels like it's more in line with the idea that the movie needs to be unpopular.