I am still no sure how I feel about this book. There were good stuff, but other times it were kind of all over the place. For a parody, it is decent.
For example, I liked that the four main characters (Oliver, Sophie, Ewan and Archie -Ron, Hermione, Harry and Draco, respectively-) had to travel to different alternative universes unwillingly. I liked that there was a dragon (Archie's mother, also unwillingly). The magic is a bit dull; if it has been more developed it would have been great.
The weakest point are the characters. Ewan was, for most of the book, insufferable. He is a disgrace for all the Chosen One. He is supposed to be the comedic part -along with Archie, who was another silly boy- but he is not really likeable. Or any of them, to be honest. Ewan hates Oliver (his former best friend in the whole world) because he stole his spotlight, so he wants some kind of revenge. Unfortunately for Ewan, to plan a revenge, it requires "brain", which he lacks of.
The evil characters were MEH, not really a strong menace.
Sophie was kind of bearable, because she is the one who resemblance the character in who she was inspired in the most.
Overall, nice world, but weak development of it.