Decent enough, but the need to click every attack, the reload times, make this par effort sub par.

I saved up for the cannon upgrade and it does crap damage with hardly any splash to make up for it. I did more damage with the crossbow and spear cause I could actually get head shots. because i saved for the cannon and got screwed on the damage I got suck and cannot progress. manual fire only works if its so you can change the force that is applies just clicking to shoot is a real pain.

Pretty darn horrible.

A lot of things you usually get standard are missing:
No autofire means carpal tunnel for all! Not only that but you can't upgrade your fire rate.
No keyboard shortcuts for Special Strikes.

While I appreciate the exclamation mark, the SS gauges look full for about 2 seconds before it appears. I've only got the first SS and it doesn't seem to do much.
If you fail a mission, your only option is to restart the mission. You lose all your money and can't go to the upgrade shop. So, passing the game is impossible. You probably have to start the game from scratch.

NITPICKS
Not necessary but an option to order your troops to shoot specific targets (eg closest to castle, lowest HP etc).
There's no story.
The king looks awfully freakish with a big head and a mean scowl.

Good man!
Nice!

I will have to echo the other comments. too much clicking and underpowered upgrades. perhaps allow player to keep some of the gold from levels they do not pass?