Mart, one thing I love about posting pictures on the net is when people tell me what is right and wrong with my work. I learn so much from what is wrong it's not funny. As long as people tell me why...not just what.
Give your sensor a good clean to get rid of those horrible dust motes. They do distract. Looks like a bit of field curvature in the corners. Polar alignment off? If that's not it, maybe it's coma thats could be corrected by a flattener?
Other than that, I would say that's a very good image mate. Colour balance looks fine and focus is nice and sharp. Great details captured and it is vibrant with good contrast.
I rate it
Baz.