Resist or Serve is a fantastic book for X-File fans and I definitely recommend it if you're a bit of an addict. The book goes into great detail about each episode of season 5, and is like having the scripts for all the episodes in one volume. It's great for reference, especially if you're trying to follow the mythology. The book also has cool background notes about things that happened during filming, which is actually quite amusing, and loads of pictures and photographs (coloured ones in the central pages). To top it off, you also get to find out what happened on the last day of filming in Vancouver before they moved to LA.
This book sort of follows on from The Truth is Out There (seasons 1 and 2), Trust No One (season 3) and I Want To Believe (season 4), but it works well as a stand-alone if season 5 is what you are interested in. Saying that, however, Resist or Serve does contain a summary of all the episodes in seasons 1-4.