Content
The screenshot isn't showing off the map very well. However, the description is pretty detailed.
I must say, that's some decent read-me file you got there.

Theme
As I can't check out the map right now, I'll give feedback from the screenshot. The theme doesn't come trough very well. The main reason why similar themed maps are looking like being in a glace is because it's better to show off the theme in fat letters, rather than confrontating the players with a not really a certain theme (which like it is now).

Texturing
The texturing is pretty plain and monotone. Try to use more texture combinations so it creates a less boring look.

Geometry
The geometry is pretty efficient.

Lighting
The lighting isn't great at all. There are several light-entities which really aren't matching the light-source which they appear attached to.
The atmosphere of the map isn't that great either.
Having a lightprecision of 32 isn't necessary on this map at all, especially because the lighting seems pretty smooth in contrast. Putting it to 64 would be more recommended (to reduce the file-size; 1,9Mb for such map is a lot actually).

Detailing
There are a lot of details which are overused. The only proper detail is the broken arch on 1 side of the map.
Even the skybox shows off there should be some mountains around, the map shows off there are just a very few. This creates a pretty unrealistic situation. So what about adding some more rocks around the map?

Clipping/Noclipping
The clipping isn't that great. In some cases, you've overclipped geometry (as the diagonal walls next to some arches), while the map is still missing a ceiling of clip (you still are able to get onto the clipping material). Some details could also be noclipped, to get some better flow.

Flow
The flow of the map isn't that great. There are several heights in platforms and areas, but they are all just long straight and flat; which creates a pretty boring result. What about cutting some of the platforms down by adding another height or some walls and such?
Why is a jumppad placed on a mountain?
There seems to be some icy wall inside the castle, but there isn't any reason why it exist (especially because it's very near a torch).

Gameplay
The pickup placement isn't good also. Pickups aren't meant to be putted away in a corner, but more to be putted on some place where people could actually overview them and add some strategy to obtain them.
The amount of playerstarts isn't bad, but could be a little more also. Having 22 playerstarts around such map sometimes feels a little low.

Overall
I've seen better castle-maps around with the same secondary theme. Keep it up and it could look similar to those others.

How about you take the stone brick texture you have right now and try to blend some snow on it, to actually make it match the theme of the map? :P