Shrinking??

I just finished The Dark Ground, by Gillian Cross. 
I'm not sure what I think about it.  I really didn't enjoy the writing style, but not sure why. 
The story is interesting, but confusing.   The main character, Robert, looks in the bathroom mirror on
the airplane he's traveling on with his family and sees a small boy in his eye.  He touches the boy in the mirror and he is suddenly a tiny little guy, smaller than a beetle, in a forest near his home.  Huh?
The giant sparrows try to kill him, food is scarce and hard to get.  He finds a little colony of other kids who were shrunken and becomes a powerful part of their society.  I am not sure I get it, and I like strange.
I might read the next book in the trilogy to see if it sheds light on the story. 
Has anyone else read these?