I read "A Princess of Mars" because they're making a movie; I read the second book (Gods of Mars) because I was interested in the series. I think I read "The Warlord of Mars" because it was free and I had it on my Nook ereader -- it's not quite up to the standard of the first two. The Warlord of Mars has an "epic" feel about it, but it's fairly short, and ultimately felt a little thin. Still, Burroughs' Mars series are pulp sci-fi/planetary romance classics, and there is adventure galore in these books. I wish I'd read them as a kid, where some of the more glaring problems wouldn't bother me as much. This is still fun stuff, and because the series is available from the Project Gutenberg site for free (multiple ebook formats), it's also a a lot of bang for your non-existent buck.