This was really fun! I really like the simple but streamlined sprites, and the music is integrated really nicely too! I'm always a sucker for island / tropical settings in games, and this one did a great job of setting a perfect relaxing atmosphere.
Some other comments have mentioned that the enemy AI could be tweaked to improve the challenge, but I wonder if it could also be interesting to add either more monkeys or a damage system where it hurts to contact the enemy. That could also add some spice to the gameplay loop without necessarily needing to enhance the AI too much.
Great work!