Feels a bit like pacman.
Takes a while to farm for upgrades and you can only farm in the early levels. No upgraded enemy that is worth more points and really no point in farming for upgrades.
Mandatory pay to finish level felt bad.
The rock level just felt like it was designed to waste time. It wasn't particularly challenging, just lengthy to go all the way to the end and then back.
Last level is just black. Nothing tells you that it is the end of the game and there is nothing more.