It's a portal fantasy about following your dreams. It seemed pretty complete to me, not really an "intro" at all, but it's hard to criticize it for that.
I first got Ending B, a "mixed" ending. Getting Ending A only took another 5 minutes or so. (Spoiler - click to show)There's a secret ending you can unlock by exploring the library and using the book.
The game includes a lot of right/wrong choices, where if you do something "reasonable" like listen to your doctors, the game immediately ends, and you have to go back and pick the other option. I feel like the game wants to create the feeling of interactivity, while minimizing any actual forking.
I think it's better to do as the game did early on, where you can choose a bunch of options, some of which would appear to avoid the plot, but they all lead back to the same chokepoint.
Like, maybe instead of insta-dying in the hospital after weeks of treatment, include a scene where you realize you have to escape the hospital.
Also! If you're going to have multiple endings, the game needs a "Restart" button. (I had to clear my cookies to restart the game.)