The Verdict: There is only one ur-review of Orson Scott Card's Ender Quartet, and it goes like this: "Ender's Game is an incredible and thought-provoking sci-fi novel. Speaker for the Dead, the sequel, is confusing and totally different, but still a good book. Xenocide is long, boring and has a terrible deus ex machina cliffhanger ending. Children of the Mind is just dreadful, except for the last 100 pages where the plot threads from the previous books are finally wrapped up." Reviewers who read Card's copious introductions/afterwords will add, "Originally, Xenocide was the final volume of a trilogy, but the book ran too long, so Card split Children of the Mind off. This is a big reason why both the books are unsatisfying." There may also be a caveat that Speaker for the Dead was actually not as good as everyone says it is.
In a broad sense, this narrative is true, but I'd like to offer an alternative explanation.
Ender's Game is now an indispensable part of the school English curriculum (I remember sitting in the gifted program in elementary school listening to 3 different book reports on it), and for good reason. Card writes very simply and his omniscient viewpoint is very aggressive, so that Ender's thoughts and feelings are very intelligible to a young reader. The key plot threads all resonate with gifted kids: Ender is always younger, smarter and more vulnerable than his peers, and he is always thinking of new ways to trump the established wisdom, and all the adults consider him Very Important but they don't tell him what's really going on until it's too late. (The reader, meanwhile, is also keeping tabs on Ender from the outside via minor characters.) It's also cracking good sci-fi, with a fun futuristic game/sport and a great use of space technology without faster-than-light travel and an incredible twist ending that's foreshadowed just enough. The last chapter is clearly there to set up for book 2, but it provides a nice sense of closure to the story by letting our heroes take a breather.
Speaker for the Dead is the rare sequel that is almost completely unlike the original. It is 3000 years in the future, Ender is a 40-year-old man looking to settle down and get married, the starships-and-intrigue action is replaced by ethical dilemmas and interesting alien biology, and the book is littered with thoroughly unpleasant characters to act as a foil for Ender, who is pretty much ready for sainthood from page 1. That being said, it's still a very good book, and frankly science fiction needs more books with intense character-driven drama instead of yet another version of Top Gun or Master and Commander in space. There is still a twist ending, but there's also like 50 pages of denouement afterward to set up for book 3.
Xenocide and Children of the Mind are basically one very long sequel to Speaker, painfully separated in a way that does violence to a story that already spent way too much time mired in philosophical discussions, detailed descriptions of various Eastern cultures, and characters repeating the same things they said 500 pages ago. The core problem is Card's decision to split up the books chronologically, which means that what is by now an incredibly intricate plot with dozens of characters needs to be rehashed every so often even though Card has run out of interesting things to say about it.
The split should really leave Children of the Mind the entire main plot line, which involves a government effort to destroy the planet Lusitania, which contains a deadly super-virus as well as all the main characters from Speaker plus two different alien species, and to kill Ender's AI sidekick who is jamming their transmissions. This contains Card's pet story idea that the soul is a subatomic particle, and love is a real physical force that creates instantaneous bonds between and within people. This turns out to lead to a ridiculous deus ex machina involving faster-than-light travel and the physical manifestation of Ender's good and evil sides, but still there is eventually closure for all the long-running plot threads.
This frees up Xenocide to focus on the philosophical parts of books 3 and 4, which take place on totally different planets (Planet China, Planet Japan, Planet Samoa) with totally different characters who are frankly much more interesting than listening to Ender's family rehash their grievances and their stupid decisions again. Without several hundred pages of setup, the sudden intrusion of the impossible into the frustrating and repressed life of our heroine, Si Wang-mu, becomes lively and exotic again. With some forced mystery added, the awkward side of these novels could be an intriguing surprise, instead of being rehashed in every conversation in a vain attempt to make the books on the same reading level as Ender's Game, which is not even remotely true.
So basically, I'm proposing that Xenocide could have been a really cool book, if it were totally rewritten. That's the rundown: Flashes of brilliance and some cool ideas, overshadowed by a huge cast of generally irrelevant characters, needless lengthening of the plot, and above all the bloated expansion of the final volume of a trilogy into a convoluted mess.