A very interesting take. I really liked the graphics, sort of a nostalgia trip for me. Also the characters felt rather creepy with that blocky face smiling sometimes.
I liked the environment, the diner looks good and being so bright and sterile makes it creepy in a way.
The audio was fine, could use a bit more eerie sounds here and there, but the sound when ghosts disappeared felt chilling enough.
I feel the writing was a bit all over the place. The first encounter felt nice and all, someone not sure of what happened. The waiter one felt a bit lacking and seemed to serve just for the key, could have used some more eeriness. The last one was a bit too obvious and it took a bit of the atmosphere, it just gave away the entire plot. The laughter on the end should be a bit more maniacal, and it was nice to have the face on the wall's glass (I was afraid of looking at the kitchen with the camera due to the possibility of having a face there! Would be awesome!).
The collisions are a bit wonky, as you pointed in the description. Getting the keys sometimes didn't work, it looked like I had to focus the center of the screen on it to be able to grab. Also, some of the dialogue got hard to read because I was near the ghost when the dialogue activated and I couldn't move back to make it fit better on the screen. The waiter had dialogue above me and the final guy was rather sideways. It could just go fitting the direction of the camera for readability instead of depending on the player correctly facing the spirit.
Edit: I had to mention that without going fullscreen on the WebGL version, the menu didn't appear on my browser. Seems the canvas didn't scale correctly.
A nice take on a horror game all considered.