I guess I started thinking about this with the new addition to Adams' Hitchhikers' Guide Trilogy, though Adams passed away several years ago. At the same time, there's also the example of Brandon Sanderson finishing Robert Jordan's Wheel of Time series, which Jordan unfortunately was unable to finish before he passed away. There's a couple of key differences between why I'm thrilled Sanderson is writing in the Wheel of Time series and why I'm rather ambivalent about Colfer's addition to HGttG. First, HGttG works fine as a complete series - there's not really any major loose ends to tie up, etc, whereas Wheel of Time still has major plot lines left unfinished. Second, Sanderson is clearly heavily relying on Jordan's extensive notes while writing A Memory of Light - it'll be Sanderson's words, but Jordan's story, and that does not seem to be the case for Colfer, who seems to have free reign to do pretty much anything. So there's need for the series to be continued, and reliance on the original author for the basic story. Another major series that would come into play here would be Dune, though I haven't read that series personally and thus can't really say much about it myself (I know, I should, I've been told that many times, and eventually I'll get around to it). Is there anything else that really distinguishes this type of writing, and what do you think about it - like it, hate it, what?