When I first heard the theme I really wanted someone to do the Spore cell stage again. Such a fond memory, and this takes the aspects of that (and agar.io as you pointed out) and makes something beautiful and unique.
Despite seeming simple, it drew me in and I played right to the end which is as long or longer than any other game has managed to keep me playing. And that's not just the visuals, music or commentary - the design is subtle but clean. Having the largest creatures on screen be lethal to your own predators, but not to you, gives a nice layer of tactics, and yet their visual presence still makes them scary. Hitboxes were friendly, and it was clear who were your prey or predators. Only real thing (though I didn't need it) is having a respawn system that starts you at the same stage you died at