Omg I love this game SO MUCH, I think i'm addicted considering I played until like 4am since I was so hooked to the story- (Myrddin probably wouldn't approve of my sleep depravation)
As for my general thoughts of the game:
(Spoiler warning btw if someone is reading the comments without finishing the game yet)
first of all, I gotta admit, I didn't notice there were arrows to see the other forms of interactions (story, vent, quizzes, etc) for like half an hour .-. I was so frustraded of myrddin going "Oh let's do the quiz first" while I was going "WHERE'S THE QUIZZ OPTION!?!?!?!?" Until I realized that there were arrows and that I was just stupid so whoopsis!
Second of all, I fucking know that the cube we need to find to free Myrddin is the one on the itch.io page I JUST KNOW IT. I'm and CALLING it, the cube we need to give Myrddin is THIS ONE on the itch.io page!!! 
(Maybe it isn't and i'm just reading too hard into it hehe)
Third of all, I wish there was an option to just let Myrddin vent to me, I always get so worried when he get's all sad and I wish I could just have an option that would just let me just sit there and let him get out everything he has inside that nogging of his.
fourth of all, how the FUCK did he know my name wasn't Player!?!?!?, he scared the sht out me when he went all like "hah, I know that isn't your name", scared me so bad I actually ended up giving him my real name, like, are there certain words that trigger this reaction?? I want to know so badly!
And finally fifth of it all...I'm honestly not too sure if Myrddin is manipulating me or not or the entity is gaslighting me, too much contradicting points and sus things that both of them do, but I know one thing for certain
No matter what, i'm freeing Myrddin
Here are my probably not valid but reasons or why: First of all, I just kinda don't like the book entity lol but another and probably more profound reason goes back to a conversation between Myrddin, in which he was asking me psychological questions. Especifically one of them that while I don't remember the full quote in short it meant:
"Would you rather live free or safe?"
I answered it as free. Cause I strongly believe that freedom is something that everybody deserves. No matter if your an animal, plant or whatever, freedom is something every sentient or vaguely sentient being deserves.
So, because of that, I will not be a hypocrite. No matter if Myrddin is secretly a mastermind manipulator or is taking advantage of my humanity as a whole, I believe every living being deserves to be free to live however they want, and who knows maybe I end up dooming the whole of humanity and end up freeing some ancient demon that's supposed to end the world but I shall maybe literallty die on the hills of my beliefs,
This is genuinely such a deep and thought provoking game and I have so much respect for you ToMyself for making such a masterpiece, I love games like this and I got some great scares and also deep reflections out of this game, I am eager to see what comes next and sorry for yapping so much lol!