I bought this for my five-year-old son because he's in swimming lessons and is afraid to put his head under water; he just sat down and read the whole book in one sitting.  Now we're talking about how Billy was scared, like him, and how it was also about water.  Whether it helps at lessons or not, he loved the book!  It has a comic book feel with some of the illustrations and the pages are sturdier than I expected.

I don't know if it really matters what order you read these in, but I just happen to know this is book 3 in the series.  Then Plane, Party and Move are the last three :-)...
Both my daughters LOVE this series!  My 6th grader (yes, reading well below her reading level)read the first two to my kindergartner as she took a bath and they were disappointed I didn't have more so...maybe consider the collection!  :-)

Browsing before gifting.... fun story with a positive message. I love that the monsters are introduced in the back of the book to get more acquainted with them. I would imagine each book in the collection does the same.... Darling!