Full details, including the story and a couple of PNGs of the map(s) are included in the .zip file. Highly recommended reading is the rather lengthy readme file; it'll explain the scenario rather aptly and give an abundance of hints and tips.
What I'm looking for is really advice on how to better landscape (it's rather bland at the moment) and some advice on the difficulty, as the readme will tell you. I call it Normal because I have absolutely no idea how hard it truly is; I basically stink at sieging beyond the limited AI so my guess is hardly a good estimate. However, an exerpt from the readme bears repeating:
Thank you for helping me playtest this map and give advice on improvement. As I've said, I'm just one person and not really a good player at that, so I can't balance this properly alone. :)