I had a love / hate relationship with this book as a kid and so was wary of buying it as an app. But ... it was so much fun reading it with mr3 that I am glad I did. There was lots of interaction between us the readers and the ipad which I love when a children's story is converted. It managed to convey that same sense of fear and excitement that I had as a child when it was read to me. There was lots of "YES!" and "You do it mum, I can't!".
There is also Monster 2, but Monster 1 gets the most giggles and is the most read here :)