In order of quality, the National Theater's The Light Princess is definitely at the top. I'm not a Tori Amos fan, but this was just magical. I'm going to try to go again.
Next up was Ghosts at the Almeida. I wasn't going to bother with this play, but with really sharp performances and a snappy 100 minute running time, it was actually darned good - I learned stuff about the characters I'd missed before and caught deeper levels of symbolism in the writing.
Well acted but brutal was Scenes from a Marriage. Lesson: a little communication goes a long way; too much communication can go too far. More sex is good.
Finally, I enjoyed the Union Theater's revival of The Boys from Syracuse, but it was good, not excellent. Some of the songs are fun, though, and if you're a musical theater fan (djm4?) you should probably make the effort.