Take the classic Spectrum game Manic Miner, remove the collapsing platforms and conveyor belts, and cut the number of different screens from 20 to six. You're left with Loony Zoo. Instead of picking your way through a mine, you have to escape through a series of cages in a zoo, each of which contains a number of carefully positioned platforms.
There are of course aliens to be avoided. And Loony Zoo does have one
innovation in that as you near the end of your task in each cage, a different set of very nasty aliens is likely to home in.
Loony Zoo is challenging and fun, but it doesn't represent nearly such good value for money as Manic Miner