Been there twice. Focus is on locally grown and in season food. I was last there last summer. Think simple dishes like grape tomatoes served on a pin rack as an amuse. It's been some time, so I can't remember all the dishes I had, but the main was lamb. Some of the best lamb I have ever had. The experience at Blue Hill was everything that I had expected to have at Chez Panisse (but ended up being very dissapointed with).
I hear Blue Hill at Stone Barnes (up on the farm) is even better.