I'm gonna start off saying: I have played both kingdom rush games and even paid for kingdom rush on steam, so yes, there will be MANY comparisons.
King of Towers is probably the first MMO tower defense I played which is interesting but... there isn't much MMO when the only multiplayer feature is, face opponent with unknown battle value, highest value wins. Ill just out right ignore that then...
The main game play is pretty much kingdom rush. You have four tower types, melee, archer, mage, bomb. Use them strategically to win the map. The biggest difference is where KR used stars to upgrade your towers, you collect money to fortify them, and supplies to unlock the towers which is a new twist on it, making you have more freedom of customization, granted by the end you could buy it all, it's how you get there. Upgrading defenses increases the value % wise which, isn't a bad idea, but it always feels like a lessened value and it's only on the base damage. ok you have 450% increase to atk damage, next upgrade is 3% of base value. Doesn't seem like much even if it does add up, it's getting to that point.
Also, there is no real character too it. Kingdom rush has, while limited, animated backrounds and interactive objects (exploding sheep) Plus in frontiers, there ar missions with unique actions like the pirate ship. I have yet to see a unique set piece, or interactive object, this game focuses more content vs quality which isn't bad... but the substance lacks soul.
I will not call it a blatent rip off of kingdom rush, if you do, you have a very narrow view point. However I cannot rank it as high as kingdom rush as it is the superior game and is balanced. This game you can make it unbalanced very easily, and again, a cash system that can grind you too a halt. I realize game producers need to make money somehow, we all do, but this is not one of them, at least in my perspective. Does it deserve the hate I have seen in some comments? No, but as it stands, it's not gonna earn money the same way Kingdom has, or the way it can, especially when you buy content for it, it's permanent, where this game it's temporary boosters. It's ok to play, but doesn't deserve cash. Don't hate it, but give it some life, and please... don't rely on fan service, I see the scantily clad giant chested girl at the top outside of battle... It doesn't help.