Looks nice, although the darkness of the castle (just under the dragon and in the nearby wood) could have been lighten a bit to show better detail and a shadow of the dragon added later.
A shadow of the birds ( against the castle wall) could also have been a nice addition to the image.
There is also a (very small) modern looking building off to the right, which seems to look out of place. This may have been cloned away with some of the surrounding trees.
Adding some cloud formations to the background might also have given the image more drama. As you know sky's can often then not make or brake an images impact to the viewer.
The cutting out of the dragon was done expertly and I can see no fault in it's placement, although it too could have been lighten (using the "Dodge/Burn Tool") in some areas to show much greater detail of the dragon's form.
As photomanipulations go, I've given your image an 7 out of 10, which puts it among some of the best photomanipulations I've seen here on .
I hope that you don't find my critique of your work overcritical.