My verdict: Burroughs recycles the plot of the third book —the main character's belovéd is kidnapped and he spends most of the book chasing down her captors (with the help of a noble savage he befriends along the way) to win her back, but he frequently gets lost (and also discovers a civilization once thought vanished), which was doubly disappointing for me since I was kind of frustrated with that book. Also, the ordering of the chapters could've been handled better. Sometimes something is implied in one chapter and then several chapters later Burroughs gives us the chapter where that happened. I'm not objecting to non-linear storytelling, I'm objecting to disordered storytelling. However, this time Burroughs takes a little time away from his usual fare of romance and swashbuckling to give us some rather heady sci-fi philosophy. The 'realists' and 'etherealists' that Carthoris encounters in the dead city of Lothar have intriguing world views and the very fact of their existence provides messy conundrums for their respective philosophies.
 Barsoom is the Martian name for Mars. Well, actually it's the Barsoomian name for Mars.
 Read my review of The Gods of Mars here.
 Read my review of Warlord of Mars here.
Mollweide Map of Mars is by the Hubble Space Telescope (NASA), and exists in the public domain. It is available at http://hubblesite.org/gallery/album/entire/pr1999027f/.