The last two levels are where the restrictions start making placement more interesting. Restricting the placement area really starts to bring much more interesting thought in how the monkeys should be placed (especially in the water level). On the other hand, the first three felt like anyone could just haphazardly place the monkeys and win. Coupled with that is the readily infinite supply of monkeys allowing anyone to inevitably beat any level given enough time by filling their screen with monkeys. I'd probably look to make more levels like the last two and maybe restrict the monkey count in some way besides a star rating.