I enjoyed the biography because it gave context to his interviews. He would say things in interviews that were clearly misleading because of certain things he had gone through in his past. The book highlights the reasons for why he would say these things. And if you go back and listen to his interviews you get a new take on things. It's as if you are hearing a new interview (after reading Ghost Story).
I would say that while his biography is worthwhile, it's obviously less worthwhile than his writing. And, in the end, I preferred the "Although Of Course" bio-book a bit more than Ghost Story.
I found I couldn't put ELSISAGS down -- I think it's because I so desperately want to get as complete a picture of DFW as possible and the book more than anything helped me understand what DFW was really up against w/r/t his depression and its presence throughout his life. If anything, I found that ELSISAGS demystified DFW to some extent, though maybe part of that is my getting older, too.