Very sharp for the conditions with 600mm/2X. In afterthought, you might have used a little higher ISO to get a faster speed and then dealt with the noise. Was this from a blind? Nice Image!
Congrats on getting such a clear image of a reclusive rarity for your parts! I like the low angle, good exposure, and nice marshy habitat implied. I would definitely remove the OOF grass in LLC, and the image seems like it could use a bit of a contrast boost (or at least darker blacks). Critical focus seems to be on the flank - I'd selectively sharpen the face more.