Very nice! Caveat: I've never had the patience this genre requires, and never will.
+ Top-notch presentation
+ Chill music, and lots of 'juice' effects
+ Solid gameplay loop that's quite challenging
- For a game that involves dragging a slingshot bar to ascend, the camera really should leave more room below the player. The first few jumps were especially problematic, because it was difficult to drag my mouse down far enough to gain the height I needed. In fullscreen mode, this problem is even more pronounced.
- Game balance is the biggest flaw here. The sunlight bar gives you precisely 25 seconds, which is fairly tight for the first checkpoint, and very tight for the end of the game. I don't know if you can skip any platforms, but it didn't feel likely.
- The second checkpoint isn't actually a checkpoint. It only refills the sunlight bar; you never respawn here. Between this and the short sunlight bar duration, there's only one situation where you can 'recover' from a missed jump - if you landed next to the second checkpoint. In all other cases, the best plan is to just hold Z and restart.