I first tried reading this book as a child around 15 years ago and stopped reading around 30%. I thought I give this book a second try...
It seems my younger self had the same problems with the book.

First of all I really liked the premise of three orphans going from orphanage to orphanage and finding a magical book. I also like the magical book itself as a device. But there are so many weaknesses. 

Most characters are really flat, most of the time I didn't feel any emotion from them.

Come on guys your brother is missing why aren't you more mad or sad about it?!

Also the adults don’t really care about the children and their wellbeing. There are a couple of characters who remind of characters of other classic children's books:

like Dr. Pym as Dumbledore and the villian as the Red Queen from Alice in Wonderland.

Additionaly, the plot is also a bit boring, because it happens to much. I don't know if this makes any sense haha. There is not really a progression but more like problem after problem. 

And last the "magical world" in the book didn't feel magical to me. This was a big problem. I wanted

time-

traveling to a whimsical and mystical world with magical creatures and so on.

And yes you could also have a gruesome queen in a whimsical world (see Alice in Wonderland)

 

And everything is a bit forgettable. I mean I only remembered three children going with a magical book into another world after 15 years and I read 30% of the book.

All this other stuff with the orphanage, pictures, monsters and queen I just didn’t remember anymore.

So this time I DNF this book for good.