Each stage is setup with a set number of enemy waves to survive as well as a number of milk mining kittens to protect. (psnstores.com)
The improved enemy wave system should allow for greater replay value as the game becomes less predictable. (co-optimus.com)
As the game progresses the switch puzzles become more complex and enemy waves more regular, but the rhythm and flavour of missions rarely changes. (eurogamer.net)