Sometimes my children like a book. Ok, if you are at all familiar with my two sons you might be rolling your eyes right now. Yes, Milo and Ezra are enthusiastic readers. But that doesn't actually mean that they just loooove all books. The fact is that they, like most enthusiastic readers, have developed into fairly critical readers as well.
They'll race through a book and then when you ask about it, say, "Ehh." That's good intel. I need to know that. It doesn't do to falsely praise a book to a kid.
I won't give an ehhh book to a picky reader. I might give an ehhh book to an avid reader, especially if she is impatiently waiting for a favorite to come in. In that case I am happy to say, "Listen, can I give you something to read until the next Artemis Fowl/Cupcake Diaries/Origami Yoda gets here? Here's something that will tide you over. It's ok. It's exciting enough, but it may not knock your socks off."
And she'll respect you for it - they can't all blow you away, and you're not doing anybody any favors by pretending otherwise. Especially not a kid who reads two or three books a week.
But The Tapper Twins Go to War (With Each Other) is NOT THAT BOOK. NOT, I repeat, the "ehh" book.