The bad: 
 Overextended. I mean, really really overextended. Specially the Guide note parts were annoying. Could do with 100 less pages. 
 Unfunny. Sorry Colfer. I love your Daniel McEvoy series but you aren't that funny. 
 Religion bashing. Religion bashing is low. 
 The good: 
 Writing this book. Hitchhiker's Guide really deserved a better ending than Mostly Harmless. Colfer was brave enough to give us that ending. I wasn't too fond of his book, but at least now we have a good ending and for that I am thankful to Colfer and whoever came up with the idea of adding another book to the series.