Hi there, thanks for checking out Blister Critters! The free Quickstart does tease most of the concepts in the game, but the full Rulebook is three times as long, with all of the options for animals, all of the Blister Paths in full (for leveling up and gaining fun weird mutations), a whole chapter full of Stuff (usable items, each with very simple mechanics—there are hundreds), a chapter on Producing (GMing—include rules for Beasts and Bliffs), and two different pilot episodes.
So it's really a question of what you're looking for: if you want to use the free Quickstart to make up your own stories, that can be fun. But I personally like the full Rulebook because it offers a lot more options and thoughtstarters—and, of course, rad art by Tony Grasso. I'm biased, though, and I hope you have fun either way.