Overall, looks ok, some large sightlines, though atleast you can't see all the way to the other spawn. As far as I can see, there is no real flanking routes which are genearally required in koth maps, it's also probably a bit small for a koth, finally, there probably only two paths up to the point, and any pushback class could cover the point easily by pushing the players off the ramp, you definatly need another side route or something to make it work better.
And I agree with the others, even though it's probably harder to fit in your map, spiral staircases don't really work well with fps games, try square or straight or something.