Mate we commend you for sticking with us that long! Cheers dude.
If you bring the humans to despair (when the slider is empty), you can posses them too - but the majority of the game can be beaten as the rat. I threw up an almost rat only playthrough on the page if you'd like to flick through. 
We def agree that there could be muuuch improvement in terms of the tutorial & the game to player communication. However I'm sure you can tell by the state of the current info sources (the beginning & the pause menu) how rushed we were!