I have completed all levels. It's a very nice and addicting game. And I'm trying to challenge myself by completing all levels with hell difficulty.
New levels will come with next update. Before you try the difficulty hell, I suggest you to fully upgrade all your units. And any feedback about all these levels?
Level 10 is hard. It took me almost a day to beat it. Failed so many times. Assassins sneak attack my cannon, and knights crash my defend line. Other levels are acceptable and challenging.
Level 10 is hard because it's the final level. Use your units to stand surround your cannon, so that enemy assassins can not attack it. And for the final wave of knights, I use knight to counter it. A knight can instantly kill an enemy knight with full health by using charge skill.
Adjusting the difficulty of levels costs too much time, hence some difficulty of levels are not accurate.