I liked it a lot! It has a nice pixel art style and color scheme, and the controls felt responsive. The merging/splitting mechanic was also pretty creative.
There were some inconsistencies, however. I believe the comment by HauntedQuest summarizes them pretty well, but I found another thing and I don't know whether it was intentional or not. I realized that if you jump, separate and then merge again mid-air you essentially have infinite jumps. This led to me solve the levels in a way that was probably not intended (this would be a pretty cool mechanic though if you designed levels around it). The smoothing factor on the camera follow script was also a bit too high in my opinion. It was sometimes difficult to see what was ahead because the camera couldn't keep up with the player, especially when falling.
I played in the browser version first (without audio in other words) and decided to try the download version when I'd gotten as far as I could. Just so that I could give a fair rating in the Audio category. My biggest criticism is that there are a lot of repeating audio clips without variation (I got this criticism on my game as well in regards to the typing sounds :P), such as the music only being about 2 bars long and the jumping sfx being the same every time. Something to consider might be to use different audio clips between the first jump and the double jump? Just for some variation.
With some more attention and fixes I believe it could turn out really nicely. Most games aren't made in a week after all, and this was a really solid entry. I hope you continue after the ratings are over! :)