Actually from what I have been told, and I will soon be able to confirm because I'm getting a 5dmkiii, the depth of field is actually about the same with it actually being slightly shallower by a 1/2 or 1/4 step in favor of the full frame. I know it doesn't really make much sense, but that is what I have heard from the responses to the question, "What are the advantages of full frame over crop?"
I have one... it is well worth the price even if you were to pay full price. It is sharper than the 70-200mm f/2.8L IS mkii at the same focal length. It is great in low light, and if you stop it down a little, it is incredible. Good portrait lens (though it isn't a 135), great macro, and just a solid all around lens. It is easily one of my favorites.
Fixed glass traditionally sharper than zoom. No contest.