Glob Arena was the prototype I enjoyed the most. I’ve gone back to it and filled it out with 5 more enemy types. While none of them has changed the game as much as I’d hoped, the extra variety has given it more longevity.
I’m starting to explore the idea of an ecology of creatures inhabiting the arena, interacting with one another. The first revision of the game just fills and fills with obstacles. I’ve given this one some monsters that consume others and it’s helped to maintain a reasonable enemy density in the endgame.