You know what's a great game design? Challenges that have nothing to do with the skills gained from getting better at the main game. I can't tell you how much I enjoy replaying challenges over and over to learn new skills I'll never use in the main game.
This game is good, but that's kinda all it is. I really enjoy both monkeys and upgrade games, but it feels like I've played this game before. Due to the polish involved, it feels like this was more than just an exercise to make a game. I would have liked to seen some new things or some attempts at new things if I'm going to be playing the same old game. I dunno...just my opinion. Good job, but I wish you would have tried doing something new.
I hate to admit defeat, but I just don't think there's any way to beat this game without paying for the premiums. I've tried level 11 over and over and I'm totally stumped on how to beat the turtle and the mammoth at the same time.
I'm finding a lot of success by ignoring the archers entirely. Also, make sure to fully upgrade your hero's strength...he can take giants down practically by himself.
Since I'm new to this type of game, I thought I'd give a few tips to any other new players. You have to complete a bunch of missions before you can get a multiplier that will make your score worth anything. You really need to pick up as many fire scrolls as possible. You can have all the 400 combo runs in the world, but without a decent multiplier and a fire scroll, you're not going to crack 50K points.
I have a small point of corrective criticism. I felt like the game was a bit too easy to cheat. I think I see what you're going for...spatial relationship testing with colors, which tests a few parts of your brain at once. I could be wrong about that, but it seems like I was able to cheat that a bit by moving the mouse around randomly. I really appreciate the goal of what you're trying to do. It's an awesome idea.