Well,this is a map which would gain a lot to be turn as a siege than an invasion. The map is also full of mistakes, not really bugs, but just mistakes.
Playability : I played this map several time at hard and very hard setting, but it was more to experience a new way to use tricks and test weakness than for real motivation.
The map is really a true siege, not an invasion. You start under attack, an invasion occur and game will stop when you defeat it. Management of your population, building a community, economy ect ... is irrevelant, especialy when your start with a bunch of food and 50.000 golds.
Balance : here many problem could occurs. Author did'nt restrict enough map options. He claim it's hard, but playing at very hard lead to easy victory, mostly because of unestricted option available to you. Of course no trade is avaible (despite a market place exist in the map), but you can hire about all military unit you want, including laddermen treb and tunnelers. You could for example dig a second moat just behind your outer walls when invaders fill the outside on, hire and build treb and dairy farm to launch plague cow, hire suicidal tunnelers squad as infantery, build fakes buildinds in pitched area to make fire longer, destroy unuseful building (so about all) to build killing pit ect ... ect ... ect ... My advice if I well understand the map spirit "tuen it in a siege map and disable all building and units.
Creativity : nothing special
Map design : I feel the author didn't spend more than one or two hours with landscape. A bit rough, some area have been a little worked, you have some hills, a bridge, other are flat empty meadows. Overall it lack of time and work.