Definitely bring out the main theme more.
For the first 50 seconds , I didn't even notice the melody... I thought this was just a very unique rendition.
Don't be afraid to mix things up a bit more. Once you've established a pattern, throw it out the window. Let different parts get louder at different times, throw in some new sounds when we get used to the old ones. Right now it's a little monotonous.
But all the above isn't to say that this isn't good. It's still an entertaining rendition of an enjoyable song. I expect to hear good things from you in the future.