Not too bad
I think alot of the promlem is you don't have any instructions. i mean, its pretty obvious that oyu have to find the ninjas hidden in the unns, but it isn't obvious that theres only one ninja at any one time, and that it changes everytime you find him. It took me ages to figure out i had to recheck old spots. so instead of that annoying little bubbl which keeps popping up /covering up half the frigging picture/ try just having an instruction page. Explain things a little further.
hope that helped. otherwise its actually not that bad.