I really am amazed at the angry reaction to this. What's the big deal? Colfer won't be impersonating Adams; he has his own unique and distinctive style. Maybe it's because I'm already a big Colfer fan, but I think this is great news.
I don't see it like someone else writing the 8th Harry Potter book. It's more like Sebastian Faulks writing the new James Bond book, Devil May Care. Anyone can see that these are distinctive titles by separate authors.
And I do think it's important that Adams' widow is 100% behind this and chose Colfer to write the book.
Honestly, you people are reacting like Colfer has just suggested nipple-piercing in a nunnery!