Even had Mr. Pratchett been in perfect health, I'm not sure that he would have been the right man for the job.
Let's face it - Penguin have commissioned this book to make a profit, not for the sake of "charity", and I strongly suspect that Mr. Pratchett would have wanted so much money to do it that it wouldn't have been economically viable. I'm sure that Mr. Colfer is a lot cheaper

. Would Mr. Pratchett have even
wanted the job? He has his hands full writing his own books, I'd have thought.
Neko - I've read the first three books in the "Artemis Fowl" series (there are 6 so far in total) and very much enjoyed them. They are very well-written, and cleverly plotted. I'm not sure that Mr. Colfer's writing style can be directly compared to anyone else - he's very much his own man, and the books aren't a "copy" of anyone else's.
Mr. Colfer is, IMHO, a very good writer. I'm going to wait and see what the new book is like before passing judgment. Some here appear to have already "pre-judged" the issue

.