Well...
Your lucky that this is one of my favorite songs of all time. You really need to work on the lip sync and smoothing out the movements.
The art was off a little as well. By that i mean that there was no scenery and some custom or modified sprites could have been used.
Some build up would have been nice before the main music and singing starts. Some variety in the dancing of the monkeys (or ukikis, same thing lol) instead of the same two dances.
The last detail is that when the monkey is singing in the beginning, he is shaking ever so slightly. To fix this be a little more precise with the onion skin tool. Not having this problem in the future will make your work look more professional.
I hope this review was helpful! Good luck with future projects! (and hopefully a sequel :3!?)