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.
Don't know if it quite qualifies, since it's sitting at a 61% audience score, but my favorite horror film Event Horizon has only a 33% critic score. I find a lot of good horror movies sit at or below the 60% mark on Rotten Tomatoes though. If a horror movie is too well rated, it's probably not very scary and not interesting to me.