This is very nice to hear. You've come a long way by finding it again! It's been many years now, this was actually the first thing I ever did in Unity. I'm still very fond of Increpare's narrative games, I've always found them incredibly expressive and I've learned so much from them.
This comes from a time where I was just starting to develop videogames and used to think a lot (much more than now) about what they meant for me and what I found so powerful in them.
Around that time I was also very impressed by Godard's "Histoire du Cinema", specifically by the idea of using cinema to talk about cinema, so I tried to do something similar to talk about a game through another game.
One of the things I've always been a little guilty of is to not have shared myself the source project of this game to be able to keep the loop (this game has been possible thanks to The Serpent's source project being available) but now it's too late because the project is lost in a broken hard disk.
I believe what you're experiencing is a graphics bug caused by some of the post-processing effects. When this happens, you can try to change the resolution from the pause menu, it could fix the issue.
Also, I just uploaded a new game build, so maybe if you update it it could be better.
There's been a number of users on older mac versions who have run in many different problems. Unfortunately, since I don't have a Mac, I have not been able to help :(
Promesa can be heavy for graphics card... I can only recommend you to try to update your drivers.
Let me know how that goes and please ask for a refund if you're not able to play the game!
