The progression of floating background things in the background to show height came out really great, and the number of UFOs made combo hits go off nicely, which is always a lot of fun.
I had some issues where I don't go into the shell quickly enough after shooting or something (or maybe it's just that the gravity pulls down the upwards velocity so fast he unshells again?), such that I struggled to destroy any UFOs from below at all, unless I'm bouncing off destroying another. So I had to always do a sideways or downwards attack to ensure I destroy them.
I'm also not sure how the scoring worked. I see there's a multiplier, but it seems to just always go up to 2 and then stay there for the rest of the time. (Also didn't notice it at first; a "10" or whatever popping up in the explosion might sell that more?)
Also, I feel like we talked about this in early playtests and there was a reason this couldn't be done, but having the mouse go back to the centre when the player clicks would have been very helpful. I kept going off the sides of my screen, such that I couldn't always make full stretches.
Anyway -- this came out great! There's a great satisfaction in chaining a bunch of UFO destructions, and a nice sense of upwards progress. Now you just need something at the top!