It's a great concept and starting point, but there's one flaw...
You don't need to possess anything haha, you're fast enough to just walk through on foot until the boss.
Though, if you don't abuse the game like I did, it's fun :D
Also, the sudden cut when you kill the boss is jarring. I'd add some kind of sound effect, particle, fade to black, something like that to make the transition a bit smoother.