I greatly enjoyed this game.
The worlds-within-worlds mechanic is masterfully applied to every aspect of game play: Your inventory is your world; Creatures attack you by entering your world; You can recover stolen food by entering their world after they get bored of yours and leave; You can even kill creatures by stealing all of their food. The opening quote aptly sets the theme.
The command interface (key + direction) gives the game a traditional rogue-like feel, though thankfully without as much of a learning curve. I miss the ability to idle, though it's usually possible to 'b'ash or 'e'ject something to similar effect. The absence of (direct) inventory management is also a bit of a challenge, though curiously fitting given the inability to enter your own world.
Beyond that, the game has a surprising attention to detail: Different terrains pertaining to each type of creature; Creatures with different food preferences; Rams bash!; Elephants trample!; Spiders cast webs!; Slime molds eat everything!