I loved it!
I initially thought Carl or Marina was the Phantom (but had to rethink based on the timeline :p) I liked that the Phantom was neither of them--it kinda subverted my expectations. I do wonder why those two were chosen, but I guess that'll be in a sequel :p
I loved the lore sprinkled around in the Heart notes. I enjoyed reading those. I also liked the blood ferns. The red glowy effect was super cool--the blood ferns were so pretty for something so dark lol
One thing I didn't know was deliberate or not was that the way the camera swung around made me constantly nervous there would be a jumpscare (tysm for not doing that, I hate jumpscares), or that the Phantom would be there when I turned around again. Especially when I opened the gate to the elevator, then entered and exited the lab--the camera was positioned in such a way I couldn't see. So it was actually very effective in making me very nervous that someone or something would come thru the gate I had let open!