This book is nearly a hundred years old, and back then there was very little of what would come to be called SF to compare with. It's certainly interesting to see where the field came from; Burroughs is one of the writers who ultimately inspired the genre I enjoy today. And there's certainly good action in here, and some ideas that were fresh and new at the time. But to my jaded 21st century taste, the writing is bad enough that it takes some effort to appreciate the good. The language is terribly pretentious and the dialog worse. I just can't picture, even a hundred years ago, someone stringing together such complex sentences with so many polysyllables in the middle of a fight. But ultimately, what really really hurts the book is the shallowness and absurdity of the characters' motivations and interactions. I have to consider this book as of historical interest only, because the characters are more believable in fan fiction.
5 out of 10.
**** PLOT SUMMARY -- SPOILERS ****
John Carter is prospecting in Arizona. He and his partner find a mine, but are then set upon by Indians. John escapes into a cave, where he becomes paralyzed, and then finds himself outside of his body. He looks longingly into the sky and wakes up on Mars. His superhuman strength allows him to win respect from the 15 foot tall green Martians, called Tharks. He learns their language and discovers that he has telepathic powers. Then the Tharks capture Dejah Thoris, princess of the other, Red, Martians, who are human sized and far more civilized. Through a series of ridiculous narrow escapes and feats of derring-do, he arranges to unite the Tharks under Tars Tarkas, whom he has won not merely to friendship but to the very notion of friendship, defeat the Zodangan faction of the Reds, forge an alliance between Helium and the Tharks, and win Dejah Thoris in marriage. Then we skip ahead 10 years, where we learn that the air factory has stopped working and all of Barsoom will die in three days, and for some reason it takes John two and a half days to remember that in his earlier adventures he had been inside the air factory and learned the telepathic passwords that are supposed to be known to only two people on all Barsoom. He passes out just as he's opening the last of the doors and wakes up back in the cave in Arizona. He spends another 10 years on earth, where he's very rich thanks to the mine, yearning to return to Barsoom.
Of course there's more -- I skipped a whole bunch -- but it doesn't really seem worth untangling.