I beat it on my second try, I would say what makes it easier if the fact that you have too many options to overcome the enemy.
You can make shields with engineers to put on tower to defend archers from horse and crossbowman, sometimes I feel this is so unbalanced but yeah makes your units kinda immune to damage.
I was using boiling oil the first attempt until I realize all about pitch is unlocked, you can also train fire thrower, traps with wood (you have a lot of wood to use, I was having like 400 to use)
so the crowd of swordsmen were a very easy to eradicate thanks to fire thrower and pitch.
You can also make bad things to have more production stuff like enjoying the stone that you can sell and make a lot of slinger and fire thrower (it was slow btw cuz the recruits join the castle slowly, so was actually challenging)
but i enjoyed it, It would be interesting to me to see how far I can go by limiting myself to just boiling on engineers and not using shields on towers. Without bad things I think it would stress me a little, lol.
I never had a clue what the trebuchet was built for, but I liked the ballista, limiting them was nice, as was the amount of crossbowman you could do throughout the game.
Also, I admit I was taking advantage (kinda not my fault) about the juggling of the enemy, they were moving around between the 2 entrances, I don't know maybe when one side is cleared the gate open so they return to that side, then go to the other side, over and over again while their HP going down, is an old game, we kinda expect this happing from a poor AI lol.