A few suggestions
1) adjust walk animation collision bounds
2) make the transition region on the edge of frames smaller
3) make the coins more even not clumped
4) there is a slight delay as the monkey hits the coin, which feels weird gameplay wise
I think thats mostly it in terms of things that need improvement. Obviously this game is way to simple, but I feel like this is one of your first games so I won't criticize effort/work put in. Keep working and get better.