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.
I really enjoyed the concept and story of In Time, which apparently has a 37% tomato meter and 51% audience score. That was probably the first less than 60% one I saw I particularly liked.
Edit: I take it back, I choose Elysium. It has a 59% audience meter and I frickin LOVE that movie, all the way down to the villain being super crazy and virtually unintelligible.