Ender's Game Series is a series of four books, one being a sort of prequel introducing the characters. The books are titled Ender's Game, Speaker for the Dead (which takes place 3,000 years later), Xenocide, and Children of the Mind. The books are science fiction and written by Orson Scott Card, who is a Mormon.
If you have not read the books and desire to do so, I suggest you stop reading right here. It's not that I'm going to give away any interesting plot points, but some people prefer to know as little as possible about the story. Since the stories build upon each other, you may find what I say gives you an idea of the "twists."
Ender's Game is the title of the prequel and it is here that he sets up the characters for his subsequent books. The last three books are the focus of my discussion.
In the last three books, Ender (Andrew Wiggin) is sent to a remote colony on a foreign planet. The inhabitants are intelligent creatures and the colonists who are humans are there to study them. As I mentioned Card is a Mormon. Mormon men are required to spend two years after secondary school on missions. Card did his missionary work in Brazil. He uses his knowledge of Portuguese and his loose knowledge of Catholicism when discussing the colony. I should mention that Ender is depicted as having a Catholic father and Mormon mother and was baptized Catholic although not raised that way (this is due to the crazy religious laws and population control laws that were enacted before his birth).
There are some problems with Card's understanding of Catholicism. The biggest one is him establishing a monastic/religious order. I'm not sure exactly how to describe it since it's well...weird. The "order" is made up of married persons who teach children at the colony's school. This is not weird. Catholics have lay orders or third orders and married persons join them. The weird part is that these persons are housed. Lay Catholics live in separate homes but do join each other for fellowship and prayer. The other more bizarre part is that in this "order" you and your spouse have your own cell but you cannot have sex with one another. Ever. Again. It's part of your vows when joining the "order." While Catholics will practice periodic abstinence, marriage is meant to be life-giving. Couples can choose to remain abstinent, I suppose, but Card is totally missing the point of a Catholic marriage by establishing an "order" for abstinent married persons. This is definitely not in line with Catholic teachings and not something I think the Church would ever endorse. Why he developed this "order" I have no idea. Perhaps he was trying to come up with something different for his made up future. I just think it shows a poor understanding of Catholicism and its traditions.
The other area of his books that raised huge red flags was his discussions about souls or aiua as he calls them in the books. Mormons believe that soul undergoes four stages: pre-mortal stage, mortal stage, a separation of the soul and body, and a rejoining. Mormons believe that God was a man. Not just Jesus, but also God the Father. They believe that God, the Father, and men all lived together. Men had souls prior to coming down to earth and joining human bodies. There's a movement (for better lack of word) which tells families to have many children in order to bring more souls down so that they can rejoin with God and be gods themselves (another Mormon teaching).
In Card's story, he has a being/whose soul is bound in hardware. To make a long story short, how she got there was she was "called" from the "outside" and this is where she landed. She also can go to this outside world herself. There's more discussion of how aiuas work, but it suffices to say they operate like the Mormon teachings of souls.
It should not be a complete surprise that the series has Mormon leanings. After all C.S. Lewis and J.R.R. Tolkien wrote science fiction and fantasy (respectively) which illustrated many teachings of Christianity. Some were more obvious than others. Tolkien being very diligent to make his books not so obviously religious allegory. Card is a Mormon and naturally that infiltrates his works. His fiction is not overtly sexual unlike leading science fiction and fantasy writers today. So if you are looking for a series to read that isn't smutty, this is a good one. On the other hand, be aware of the Mormon over-tones when reading the series. If you wish to avoid any Mormon-related stuff, then stay clear of the series. And be aware that his knowledge of Catholicism is short-sighted. I know the Ender's Game movie is popular, but as I said much of his philosophical and religious thoughts and writings don't weigh very heavily in the first book. If they were to make a second movie, keep in mind what I said about the books themselves when judging whether to attend the film or not.