Wonderful item. I love magic items that are strange and dangerous. It has a beautiful property of recursion, a story within a story.
To be truly devious, You could stack them up.
The first book, once a few monsters are defeated says: "And now the party, battle won, claims there treasure, a golden tome."
And then the golden tome is just another Book of Eventful Evenings.
Make it into a puzzle, perhaps every book in a massive library is one of these books, and only one book is a real book. The clues to finding real book lie on the covers of the fake books, and on the clues they give at their conclusion. Go to Comment
I like the options it leaves the dm so they can fit it into most any campaign and lead them pretty much anywhere with it. Just throw another orb at the end and they get a highlander show until just one orb is standing. Go to Comment