I think the manga did the first episode better
I get the impression that the anime chose to start at a later point and will be using flashbacks for the first few chapters of the manga.
As someone new to the series who watched the anime first and knew nothing going in, I did like how it was all set up. My reactions ended up following this pattern: "This is a little too happy... kind of unremarkable... why has no one moved from their seats all day? Why are we now in the uncanny valley? ZOMBIES and CRAZY PEOPLE!?!?! Hell yes."
As someone who read the manga, I prefered how the anime did it. I liked all the signs:
Girls reacting to her delusions, like when opening doors to classrooms.
The grave on the roof scene.
The spine-chilling message in the blackboard behind the teacher (it was quite jarring, in a good way).
A short scene where the windows were broken while still in the delusional POV.
Wondering how the story will start off from there. I am not a 1:1 adaptation purist, as long as it is good I am good with it.