I decided to give it a full playthrough to get a good feel of the game and spot bugs. At first I just ignored all the side stories and ran straight through the main plot.
It was way too fast.
Then I went back and played every side quest and optional scene.
Of course I tend to go faster than other players because I know everything. But the speed still worries me.
I'm thinking about adding... stuff. I won't extend the main plot, but add more optional content, secrets, etc. Not much. On one hand, it'll give me the opportunity to add more of the things from my Bathroom Wall. On the other hand, it will delay the release of the game a bit. Not much.