Very nice and pleasant game. Thought out mechanics, appealing graphics and good level design to complement them.
The only suggestions that I could think of are:
-Making the interactable items glow in the dark even outside of your flashlight's light, as admittedly I did spend an extra minute or two searching the whole level for the blue keycard because I missed it once.
-The cooldown on the stunning signal is kind of too long, you can especially feel it in the sections with 2 or more ghosts. But when it's upgraded to a weapon then the cooldown is fine.
-Should definitely add a prompt that says something like: "Now I should head for the exit..." when you kill all the ghosts (actually I don't know if killing all of them is even required...). It's obvious that you have to go there, but you won't do that (or at least I didn't) until you've checked if you killed all the ghosts. And the only way to do that is to walk around the whole level again.
Overall, good game!