I liked the background, and the way the trees fade out. But the tower wasn't very pretty, which is a let down.
The customization of the fortress is limited, which again, is a huge let down. I understand I can't have a Black Deathskull buried into the side of a mountain with flame coming out of the eyes. But maybe let me stick another cannon or two on, or trenches in front to slow the enemy, or a moat, or a drawbridge, or even just let me change a flag. Something.
And, as previous mentioned by a few people, the balancing is hard. I see people have beaten it, but I don't know how. I have tried constant attack, and I run out of funds. I've tried defending, and occasional attack, and I eventually was overwhelmed. I even thought that if I didn't buy a single unit, then the enemy wouldn't advance beyond low troops. I stopped creating units (except the Boss) when they had soldiers (with the shields and broadsides). They killed my boss once, maybe twice. They STILL got the catapult before I did.
Just, no. It's too hard. It's a remake of Epic War, which isn't done quite as well as Epic War. The one innovation, and I liked it, was terrain - being on high ground gives an advantage, and so on.
Other than that, sorry to say, but it's just a bland copy.
You have real potential. Either redo this, balancing it and add a feature or two. Or work on something else, some crazy original idea, no matter how stupid. I'd look forward to that.