I like all the production value touches like the double jump particles, death effect, unique menu, and various graphics. The many small things go a long way to make a game feel unique, in a good way.
I feel like this engine is a good example of adding production value, and I'd recommend anyone who's a novice at production value to download and play it. And to the creator, I wish you the best of luck making fangames, you have a good start