For me, the pose is not the best here. Although, I am happy the the beak does not cross the tail feathers. However, I thought I would post as I like the intensity of the eye. Because of the pose I am a little unsure on the crop, so any comments on that would be particular useful.
Also, can someone confirm this as a yellow-legged. I discounted a Herring gull due to the intensity of the eye ring.
Ben, nice job getting such a complete view of the gull.
I did a CCW rotation of -1.5 using the lens distortion filter in PS. I also took down your crop to a 10x7 with the ROT's upper right crossbar right at the gull's eye. You were right to put more negative space to the left as that is the direction he is looking. I think you just need a little tighter crop to bring it all together.
I also added a bit more sharpening - especially around the eye area - but he still looks a bit soft. Did you run NR on the bird by any chance?