If you've read the original novel this book provides a fascinating alternate look at the events in Shelley's book. Written in the same format, the book uses letters and journal pages to tell the story of Frankenstein from the monster's point of view. Definitely worth a read. The nature of the monster is explored, and you find out several things about the genesis of the monster that come completely out of left field.
A very interesting take on the story of Frankenstein, but be prepared for a rather odd ending.