I've reviewed a number of books from the Spot series on Amazon, and I'm always positive about them. When my daughter was younger, she loved Spot books. My son, who's 2, loves them now.
In 'Spot's Birthday Party', there's a game of hide and seek. The guests at the party hide, and the reader helps Spot find them by looking behind the flaps. There are clues as to which of Spot's friends are behind each flap (e.g. banana skins on the page where the monkey's hiding), which adds to the fun.
The Spot books are enjoyable to read and made to last: even the books my daughter looked at five or so years ago are still in good condition.