I was thirteen when I first saw The Princess of Mars (with the Michael Whelan cover) at the bookstore. Monsters, swords, barbaric splendor and a beautiful naked woman... what more could I want! And I read it, reread it, and reread it until I found The Gods of Mars and The Warlord of Mars. Forget Narnia and the Shire! Then came Thuvia, Maid of Mars and The Chessmen of Mars. Man, I could not get enough of Barsoom! (By the way, Barsoom is the Martian name for Mars.)
That is until I was looking for more Burroughs and I came across the Frank Frazetta covers of Conan. The narrator of A Christmas Story says, "Only one thing in the world could've dragged me away from the soft glow of electric sex gleaming in the window." Well, only one thing could've dragged me away from the softly hinted sex on Barsoom... and that was the hurriedly gratuitous sex in the Hyborean Age. After reading all of Howard's Conan tales (plus those by Carter and de Camp), I read The Lord of the Rings. By the time I returned to Barsoom, it was no longer overly exciting. I went ahead and finished all the books. But the first five books of Barsoom are by far my favorites.
Back in 1979, I did not know Burroughs originally wrote the stories as serial installments for magazines... but I loved the cliffhangers at the end of chapters.
I can see how A Princess of Mars would have been complete in and of itself, if it had not made money. As the first sci-fi that I read, it was magical. I was transported. I'll always have fond place in my heart for Barsoom.
The next two books, Gods and Warlord, fleshed out John Carter's story into a planet spanning trilogy. It went beyond the Red Men, the Green Men, and the White Apes. All of a sudden there were Therns, Holy Therns, the First Born, and the Yellow Men of Okar. John Carter had to deal with false religions, slavery, Carthoris, naval battles, and a giant magnet of doom! It was great.
Thuvia and Chessmen were both retellings of Princess, but with different protagonists and damsels. In both of these, I think Burroughs really hits his stride. He does not have to give any introductions to Barsoom, but hits the ground running. For me, the entire high point of the Barsoom stories is when Turan the Panthan (aka Gahan of Gathol), a Red Martian without John Carter's super abilities, leads a team of slaves in a bloody game of Jetan (Martian Chess where the losers die and the winners get the women) in an attempt to rescue Tara of Helium.
If you've never read sci-fi, if you are thirteen years old, if you grew up in a strict/religious/conservative home, then I think you might enjoy a trip to Barsoom.
I tried Tarzan. I read Tarzan of the Apes twice and The Return of Tarzan once, but they never fired my imagination like John Carter.