I didn't get to read the full book, just an excerpt from the publisher.
Dad is Fat is a great extension to Gaffigan's stand up. It's definitely his voice, just a bit more serious. In the bits I got to read, he wrote about the friends who started families before he did, what life is like when you consider Central Park your backyard, and a whole chapter on candy.
Anyone who enjoys his standup should give Dad is Fat a read.