Yeah i wanted to make the worlds more different, but time became an issue, so it became out of scope for me. Been gathering ideas over the last couple of days for how I might do that :).
The spawn rate of the asteroids/etc increase over the course of each level, so you WILL have to hit that button to clear them out eventually. The trouble is when you do, the timescale gets quicker, so the game speeds up a little (and I extended the button ready delay a little each time to).
Thanks for playing, glad you enjoyed sending cute animals to the farm :D. And glad you liked the "notes" to :).