These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Anvilicious: Global warming is bad (book four). So is pollution (book five).
Big Name Fan: The series has a few. Most notably St. Fang of Boredom and PhoenixFanatic.
Broken Base: Oh boy. To some the series ended at book three and everything else after is just not even considered by some to be existing.
Canon Sue: Maximum Ride herself. She's got fantastic leadership qualities, good looks, kung-fu abilities, and super speed. No, really. And she dates Troubled, but Cute winged boys.
Angel is ridiculously Sue-ish. She has the most extra powers of all of the flock (and will just get them for no apparent reason), she is described as cute and blond and angelic and sweet. Everyone who sees her loves her (except for the evil scientists). Of course, there are the hints that she wants to take Max's place as Flock leader and that she apparently sees no problem in mind-controlling people.
By the fifth book, the bird kids as a whole are a Mary Sue, particularly since the fifth book features several chapters showing trained professionals who have spent possibly years of their lives mastering advanced skills in the arts of combat and stealth finding themselves inherently inferior to those great bird kids to a ridiculous degree, all to show that these kids have absolutely nothing to learn from adults who are presumably experts in their field and are clearly wrong to attempt to provide these children with any kind of instruction.
Adding to the former, the kids starting to develop even more superpowers and being portrayed without many major flaws is shoving them even further past the border of Mary Sue-land.
Cliché Storm: From the evil twin and the stereotyped characters to the boy drama this series uses almost every YA Fiction clichés known.
Creator's Pet: Angel, though widely disliked amongst the fandom, constantly gets a bunch of powers, and is now apparently going to get her own book, Angel: A Maximum Ride Novel.
Critical Research Failure: Anyone who knows anything about Game Boys could tell you that they don't have downloadable games, and certainly wouldn't have a bunch of them pre-installed if they did. And that you don't sell the display copy of a game console.
Deader Than Disco: Due to the series' abysmal second half. It's almost impossible to believe that a movie adaptation was considered at one point.
This may change now that the final book has revealed the Voice to have been Angel the entire time...
Fanon Discontinuity: Some fans choose to disregard the 4th book altogether. The 5th book could well end up with this status too.
According to most fans, the fifth book (apart from the title) is better than the fourth, but not as good as the first three. It could be the fact that Fang and Max get together. God knows how long it'll last. In the 6th book, it gets put on hold, and in the 7th book, it seems to bepermanent. Of course, there's always the last book, though.
Hilarious in Hindsight: School's Out Forever has a scene where a kid at Disneyland mistakes Ari for Wolverine and asks for his autograph. Disney bought Marvel several years after the book was released.
Interestingly, both are given Take That, Scrappy! moments in the final books. Maya has her throat torn out by a cloned Ari, and Dylan goes berserk, terrorizes a city and tries to strangle Fang.
Shocking Swerve: Virtually every twist in the series applies, but the one that really takes the cake is Mr. Chu being some sort of... alien... thing wearing a Scooby-Doo-style mask. This was never explained, or even mentioned for the rest of the series. Shocking Swerve indeed.
Squick: Roland suggesting that the under aged Max and Dylan (who is really 8 months old) breed together. Not later when they're older, no they should do it right now. He even has a home set up for them already, not to mention how Jeb agrees with him. Thankfully Dr. Martinez goes Mama Bear on his ass.
Strangled by the Red String: The series started out with just the gentlest of implied romance between the two main characters, focusing mainly on an intricate plot revolving around the mad scientists who created them. Then book four hit, the plot disappeared, and suddenly they were all over each other, all the time. The fandom was thrilled for the most part... except for those who realized that these two characters were, for all intents and purposes, brother and sister...
Strawman Has a Point: In the fourth novel, Max is furious that, after she and the Flock come to the government's attention, they would dare to try to put them in a boarding school. A few of their concerns — being told they would be studied to a certain extent, etc. — were valid, given their history. Several others not so much, especially when Max basically tells them "we've had it harder than you and we know better". It's kind of difficult to argue that they are properly prepared to move to civilian life when they decide to dive-bomb the Pentagon for amusement and then are surprised that there's retaliation.
What an Idiot: In book three, Max decides to have Dr. Martinez surgically remove a microchip inside her arm to get rid of the Voice, knowing that she could risk losing the ability to use one of her hands. So Max decides to go through with the procedure, and lo and behold her left hand goes slack. Not only that, but guess what? THE VOICE HAD NOTHING TO DO WITH THE CHIP IN THE FIRST PLACE! Max just gave up a perfectly good hand.
Tearjerker: Ari's death, especially Jeb's reaction towards it.
Ari's funeral counts as well, with Max, the Flock, and even FANG showing emotion to it! It is a surprisingly poignant moment.
The Woobie: For some, all the shit Ari's been through can really tugs on one's heartstrings. He's seven years old.
Iggy also counts as well. At first, being blinded by the mad scientists of Itex doesn't seem to faze him... until in the second book when he breaks down after the Flock's failure of not finding their parents when he confesses that if he would ever lose the Flock, he would lose himself. Then, after that, when he is finally reunited with his parents, it looks like they will accept him for who he is... until it turns out that they were planning to expose him to the world, basically gaining money from him and not even caring about what he thinks, forcing him to go back to the Flock. Poor kid.
Really, the entire Flock also counts as well. From Nudge's desire to understandably be normal, to Gazzy and Angel being sold for 10,000 dollars by their own freaking mother [[not to mention Angel being tortured at the School...]], Fang finding out that his mother was a drug addict and having Mayadie in his arms and Max having to struggle with saving the world and being betrayed by the people she loves the most. Granted she may Wangst a lot, but can you blame her?
Considering all the crap they go through, they can also be considered Iron Woobies.