Heyo, checked out Dun Bhirum. First of all, nice unusual layout and class job on the texturing and surroundings. Nothing wrong with it really. There are a few pebble texture errors, as in random high weight slabs pieces of pebble, but I am very familiar with those so can't ask you to try to fix them. The door on the left side when attacker is a little too small for the doorway, there is light glinting past it on 3 sides. Really just nitpicking though.
I am slightly worried about balance. It took me 30 seconds to walk to the winch when the doors fall with the quite slow hosting character and 35 seconds to the flag. 35 seconds to the flag is good, if it weren't that the defenders probably spawn further away than 5 seconds from the flag on average. Although defenders do spawn close to the route that the attackers have to take to get to the flag, so they might slow them down, but it will be very hard for any far away spawners to save the flag when it is already in peril. Now I get that the point is that losing the winch makes it hard for defenders, but the winch is quite hard to hold for a prolonged time if you ask me. Especially because the backway proves a danger from the back at all times.
Although I have no idea what the corresponding walk timers are for Sea Raid, I could imagine a bit longer with the ladders, the thing is that there is a long narrow street up to the flag. This street causes these intense late round fights where if the defenders kick ass, they can still win. Relatively few defenders can stop the quick stream of attackers. It is a lot more open for your map, making an opened gate much more a game of numbers then in Sea Raid. A game which I fear attackers will win, as I think the average cRPG character is a little faster than 0 agi, 0 athl nude. Defenders simply won't be able to keep up with the attackers spawning.
This is of course my uneducated opinion from walking around in the map with which you might disagree, I am willing to give the map a try anyhow, but I think balance would benefit from either a longer way to either the flag or the winch, or harder chokepoints to either the flag or the winch. Fill some of the streets with more crud, prevent the attackers from being able to push at a crazy rate. It is fine if an opened gate means almost a certain loss for the defenders, as long as the winch is very defensible. It is also fine if the winch gets opened early which opens a straight route to the flag, as long as this route is defensible. It is up to you, but in the grand scheme it should be harder to attack.