This is a really good game and fun to play.
It seems simple, but there are a lot of gameplay mechanics to explore and you gradually add new ones every few levels. Essentially flawless as well; I didn't notice any bugs.
If I were you – since you already have medals in the game – I'd add a couple more to keep the players captivated (e.g. a medal for progress every six levels). If they feel like quitting the game, but it's "just two more levels" till the next medal, they might just as well pull through.
Also, I'd make the hook shooting and reeling yourself in faster. At times, I was awkwardly wiggling myself out of a tough position because I didn't want to risk losing all my progress in a level because it's almost impossible to regrip the same spot you just left. It also makes the swinging harder. But perhaps, that's the part of the game's difficulty and it's up to you, after all.