This was my first book by John Green, and I must warn you now that I gobbled up every book he wrote in the coming months. Alaska was definitely somewhat of a dark story, as the entire second half focused on boarding school students contemplating whether or not their vivacious (and depressed) friend Alaska had or had not committed suicide. Great, great book; I highly recommend it (and anything else by John Green).
As a side note, I listened to part of this one on a Playaway and highly recommend the audio version--the narrator was excellent.
For a more complete review of this book, check out Bookshelves of Doom or Kirkus Reviews.