Well, we've reach the final entry in the series...
In the first of two adventures included, Dejah Thoris is kidnapped while out for a ride with John Carter. A ransom note is left demanding that their iron mines to Pew Mogel, a self-proclaimed "most powerful ruler" of Barsoom. When John and his friends attempt to rescue her what they find is a mad eye popping villain, an army of intelligent white apes and Joog-a simple minded giant under his control. With Pew and Joog heading for Helium, John has to save the day-and that includes dancing ulsios and a lot of silliness.
After that adventure John Carter hopes to have some peace and quiet when he is summoned by Tardors Mors. But it's a trap and he's for once abducted by skeleton like creatures from Sasoom-better known as Jupiter. When their mad leader decides he wants Barsoom for himself, John must act to save his adopted home world and his incomparable Dejah before it's too late. Will he stop the Skeleton Men?
As you can tell by the two plot descriptions, John Carter of Mars isn't a complete novel. Instead it collects one finished novel and an unfinished one, both published in magazine form during Burroughs' life but not collected until nearly 15 years after he died. The first entry John Carter and the Giant of Mars also bears another distinction-it was the first John Carter story not written by Burroughs but by his son Jack for a planned entry in the Little Big Book series (a popular children's book series that had illustrations on one page and the story on another.) Ultimately Burroughs senior did some work and it was published in 1941 and it shows why his style was hard to imitate. Also it suffers from many errors with regard to the previous novels and just never overcomes the fact it was written for small children. They might enjoy it but the older reader probably will just laugh.
The second story-The Skeleton Men of Jupiter-would see print in 1943 but Burroughs never completed it. In some ways maybe it was for the best-Skeleton Men is predictable and unsatisfying and repeats some of the same problems as the last two novels. What really does this one in is the lack of suspense. By this point we know John Carter will escape, rescue Dejah Thoris and save the day but it never felt this worn out before. Some have speculated that Burroughs never finished this because even he saw it as poor compared to the previous entries. It might have picked up in the second half though. But we'll never know.
So the final entry gets a collective ** out of 4 for both stories.