I am a huge fan of the books.
I give it a B+. It was a visual and action spectacular - but the plot and dialog suffered from a severe lack of ERB magic.
The actual plot of “A Princess of Mars” was much more simple, and at its heart about the love between a man and a woman, and the friendship between two people of different cultures and races. “John Carter” was about a civil war veteran figuring out that there were still things worth fighting for, and getting over the death of his wife.
Making Dejah Thoris a warrior-princess was not a major change and I had no problems with it. In the original stories women were trained in science and culture and arts - while men were trained to war. But there were women warriors in one of the books and I didn't object to the fiercer Dejah.
What I did object to was her fleeing the arranged marriage her father/grandfather set up for her. Thados Mors, the jeddack of Helium and (in the books) grandfather of Dejah directly stated in the books that he would rather see all of Helium reduced to ashes than to sell the honor of his granddaughter to Tal Hajus the Jeddack of Zodanga. Dejah took the sacrifice upon herself, thinking John Carter dead in the pits of Warhoons. When John Carter found out she was betrothed she said “I can never be yours while Tal Hajus lives.” John replied “You have signed his death warrant my princess - SAB THAN DIES!”. “Not that either” Dejah replied “according to Martian custom I could never marry the man who killed my betrothed.”.
MUCH BETTER IN THE BOOK!!! Seeing Thados Mors willing to sell Dejah to save his city really got under my skin. Why the change? What purpose did it serve?
For no good reason they also changed the story of Tars Tarkus. In the book he was a chieftain of the Tharks under Tal Hajus (the Thark with the broken tusk). Tal Hajus tortured to death the secret lover of Tars Tarkus - the mother of Sola. Tars wanted nothing more than to challenge Tal Hajus and kill him. So much so that when John Carter has the chance to kill Tal Hajus he denies himself the pleasure to keep that option open for Tars. Tars takes it, and DEFEATS Tal Hajus in single combat. Resolution!
In the movie he was the Jeddack of the Tharks - Tal Hajus was the subordinate who wished for an excuse to challenge. When they fight Tars Tharkus, acknowledge in the books as the greatest warrior among the green Martians, is apparently defeated by Tal Hajus. And when John Carter beheads Tal Hajus, John Carter apparently becomes the Jeddack of the Tharks.
Why the change?
And what the hell were the Warhoons (another tribe of green martians) even doing in the film if they were not going to actually fulfill any purpose in the plot?
The actual plot of “A Princess of Mars” is so simple as to be almost simplistic. That people found the plot of “John Carter” confusing doesn't speak well of the adaptation.
In the books Mars was a dying planet kept alive only by the constant efforts of the red martians. Dying because of its size and age - and the fact that its atmosphere (and water)was bleeding off into space.
In the movie the Therns (who were reserved for the second book), for some inexplicable reason, wanted the planet ruined - and enlisted the Zodongans as their pawns.
A few other nitpicks. John Carter could make some incredible leaps - but the movie made it look absolutely superhuman. Woola the martian hound looked way too much like a dog and was shown as being superfast - not just the fastest animal on Mars - but a superhuman speedster. The two moons of Mars are always shown the same distance apart and not moving. On Mars the smaller moon absolutely races across the sky - and ERB mentions it about a dozen times - practically every time there is nighttime scene.
I meant “Sab Than” the Jeddack of Zodanga in the 6th paragraph, not “Tal Hajus” who was the Jeddack of the Tharks. My bad.