Based on the movie: Lord of the Rings - The Two Towers, specifically the battle of Helm's Deep
Keep Aragorn, Legolas and Gimli alive in the battle until Gandalf's promised army arrives.
Though the trio are very strong, they are not invulnerable. Use them carefully.
Legolas: Long range yet strong archer. Weak armor
Gimli: Medium range (Throws his axe). Medium armor
Aragorn: Hand to hand combat, strong armor, stronger attack
*I tried to make the fortress and walls as look-alike as the one in the movie
*I also added the cliff where Gandalf's army/reinforcements comes from
Playability: This was Lord of the Rings, which boosts your score, but this scenario itself wasn't that fun. You don't do much, and the heroes are so overpowered that you can just leave the room, come back 15 minutes later and you've won with no damage to the heroes. You also should've just set out all the enemy units rather than using the trigger looping...in LOTR:TT, enemy Uruk-Ai didn't just pop out of the ground.
Balance: I mentioned alot of balance issues above. The heroes are too overpowered, you don't do much in this scenario and it's very easy to win.
Creativity: You put effort into the walling and cliff schemes to make it look realistic which was nice. You also used some good units for the enemy. But, how about a place where all the unarmed citizens of Rohan stayed? You should've made a bunch of female villies and hid them somewhere; little details like that.
Map Design: Pretty good. The walling was good, nothing else notable other than that...
Story/Instructions: Instructions are fine. You could've gone into depth with a story; I guess you assumed everyone knew about Helm's Deep before hand...You should've put a good story description in.