I like the design of area 3, with the assumption that a map will be added at some point. An non-linear area that large with backtracking is a bit of a nightmare with no map, especially if there are gaps between play sessions.
Also the game loses fullscreen whenever you close the game or load a save, and I kept getting a slightly moving seam that stretched across the screen, both on fullscreen and windowed.
The acid damage upgrades scale up a bit too fast for the current enemy health, and while rapidly digesting enemies can be useful it's counterproductive with the healing/stamina regen for active prey as well as the offensive burp. Plus you get less time to see the animations of having live prey. Not a major issue but after getting a number of upgrades in it I ended up feeling like I'd made the game less fun for myself.