Great look-back preening pose, lovely iridescence. I love the swirly water patterns, especially the green on the right. (Wish that had continued through the left as well, but a fine frame nonetheless.)
Critical focus looks to be on the upper back, but the detail looks pretty good across the whole bird. I'm always looking for a bit more profile, but this does show some nice action I'd miss in my usual poses (it's all personal preference). Water is pretty cool though I prefer the green/right half to the left/blue.