I really like all the fancy lighting and attention you devote to little details in that regard. The piece looks pretty well balanced in terms of color and lighs/darks as well as composition too.
Pillars - (or whatever you call those rectangular protusions - im not good with architecture,sry :s) - on the big blocky structure on the left side of the castle DO look copypasted though - it kinda messes up the perspective of the thing and makes that section look a bit crooked.
And the other thing is that there's something off about the raft too - I'm guessing it probably has to do with perspective too.
Otherwise - Well done; and good luck with the CoTM!
Cheers m8.