So the skybox and the crows kick ass. The whole castle thing you got is really nice, good consistent theme. But there is limited options available for flow. It's too linear, save the fork split past the (currently broken in svn) doors. The pit in the center with the tele's from under the flag holding the sniper is a good touch.
As I said in the 'need more DM/CTF maps' thread, I'd like to see more changes in altitude. Altitude is one of the fun ways to gain speed, that or enough health to rocket/mortar/laser jump.
I think invisible walls suck! I don't agree with the limit space you've given us to play in this map. The screenshot below shows where the invisible walls are:
I'd love to see instead, the castle exterior built up, creating a ceiling and an outside we can play on. Maybe have some holes in strategic places for us to drop in. This helps the changes in altitude problem as well.
To also improve the altitude changes, I propose 1 or two towers on top of this part:
And finally an added path way that leads to a room of some sort here:
To wrap it all up this castle needs to be somewhere, on a giant mountain? In lava? In a volcano?
Hope this helps.