Backed by the Pentagon: Somewhat odd, considering almost every Decepticon from the first film was a military machine, and the Pentagon typically doesn't support scripts that make the military look bad. The fact that the US Armed Forces kick a considerable amount of ass in all three movies, and the movie producers pointing out that the Decepticons picked US military machinery because it kicked the most ass, is what convinced them to sign on.
In a directing version, Michael Bay has directed many car commercials in his time. His base understanding of how to film and light cars on camera made him, incidentally, ideal to teach CG animators how they would look.
Most of the military extras that shows up are actual military personnel. Most of the time, they don't even have a script beyond director Michael Bay telling them to say and do what they'd do in the situation.
Megan Fox has had a history of badmouthing the series and its director, and behind-the-scenes drama (most notably her saying Bay had a Hitler-like dictator persona on set and several members of the crew responding by anonymously praising Bay while bashing Fox in an open letter without Bay's approval) was why she did not return for the third film.
Many of the major players of the film series have expressed regrets towards Revenge of the Fallen. Michael Bay in particular apologized for Revenge of the Fallen, and promised better results for Dark of the Moon.
Eventually the franchise became this for Bay. He was essentially forced to keep making sequels like clockwork, and being unable to make a more personal movie until the franchise took a three-year hiatus. Ironically and hypocritically, executive producer Steven Spielberg, who bemoans the lack of originality in Hollywood, pressured Bay to keep making more sequels.
Downplayed with Hugo Weaving. After the films were done, Weaving said that he wasn't invested in his role as Megatron, but expressed genuine regret that he didn't care too much for the role that is so beloved by fans. Michael Bay was offended and sniped at him for the backlash.
In a rather late addition, Travis Knight revealed that he disliked Michael Bay's take on Bumblebee.
Peter Cullen has expressed dismay at some of the more aggressive lines he is given as Optimus, and particularly singled out the line in Age of Extinction where Optimus vows to kill Harold Attinger as the line he felt was the most out of character. Peter has remained a trooper and does as asked, but he's expressed sadness at the more aggressive Optimus we see in the sequels.
Creator's Pest: Michael Bay has gone on record to say he hates Arcee, and happily killed her off, without much of a sendoff. He even openly said so in an interview prior to Revenge of the Fallen. IDW stuck a big middle finger up to that a few years later in their Dark of the Moon prequel comics by having all three sisters as alive.
David Wise, one of the writers for the original Transformers cartoon, has a bone to pick with the films. He feels that they have less story and characters than the show he worked on, and has questioned the portrayal of Optimus Prime, mainly him executing Sentinel Prime in Transformers: Dark of the Moon. He compared the original Optimus with Abe Lincoln, and responded: "He's got to have malice toward none. And Abe Lincoln doesn't just up and bust a cap in a dude's ass because he was a turncoat." He told Michael Bay "Leave my stuff alone!" in relation to both the original Transformers cartoon and Teenage Mutant Ninja Turtles (1987).
Doing It for the Art: The movies exist to sell toys, GM vehicles, and many other products, but Michael Bay didn't want to do it at first. Yes, Mr. Flash Cuts & Explosions had to be talked into doing this. Bay explained that the only thing that made him even bother to consider the job is that you don't just ignore an offer from Steven Spielberg. Once he went through "Transformers School" at Hasbro, he had a wave of inspiration that was about showing something no one has ever attempted to do before. Once convinced, he made sure the CGI was some of the most detailed ever made. Industrial Light & Magic actually said they hadn't done work this groundbreaking since Jurassic Park.
Devastator is likely ILM's greatest accomplishment to date. The scenes with him had such a massive level of detail that rendering him took the ILM equipment to its limits. "Took the ILM equipment to its limits" as in smoking and melting one of the motherboards. Also prior series just made a blur of motion between the transformations, sort of "cheating" the process. Here no two transformations are identical (same basic components go to the right place but how it does that changes) and each one is appropriate to the scene, sometimes done in slow motion for dramatic effect.
Bay insists on doing as many shots for real as possible, instead of doing everything in CGI. He rarely uses a blue screen. That really was the Hoover Dam, that was a real bus splitting in half, those are the real pyramids, that was a real sand explosion, there is a real life-size Bumblebee prop, the entire city of Chicago represents itself, etc.
All of this can be evident in the scene in the first film where Sam is searching for his glasses and the robots are in the backyard. The visual effects were not cheap and that entire sequence was comedic in tone (Steven Spielberg even mentioned, while laughing, that he had never seen something like that before). But it also provided some of the most characterization for the robot heroes and helped to make them more than the killer robots everyone were afraid of, so that when they come to Sam's rescue we are rooting for them.
Bay had to be coaxed into making the third one in 3D, because he said it was "gimmicky". Seriously. And when the decision was made, Bay refused to work with anyone but the best. The best being the crew behind the 3D in Avatar.
Enforced Method Acting: Most of the stunts were performed live, with no CGI. While safety measures were put in place, Shia LaBeouf was really holding onto a statue 20 stories up and the actors were fully briefed on what kind of explosives were used to create the Scorponok sand explosion.
Frank Welker replaces Hugo Weaving as Galvatron's voice. It's unknown whether this is intended to be an in-universe result of the new body or just a plain old case of The Other Darrin. The fact that he is back as Megatron in the fifth film implies the latter.
In Dark of The Moon, Sideswipe is voiced by James Remar instead of André Sogliuzzo. In a confusing audio mix-upnote and if one pays attention, was clearly animated to say it Barricade spoke with Soundwaves' voice, thus technically Jess Harnell was replaced by Frank Welker.
The video games based upon the films often have different voice actors for several characters for cost reasons or due to the movie's casting of a character for the movie proper not being revealed until it's close to release or already released. However, it seems that if Optimus is in some tie-in material, you can expect that Peter Cullen will voice him.
Playing Against Type: Mark Ryan previously voiced the heroic Bumblebee and Jetfire. Now he voices Lockdown, a cold, fierce bounty hunter.
The Red Stapler: There has been an increase in the popularity of twin black racing stripes for custom paint jobs, whether or not they are yellow, Camaro's or even sports cars.
Show Accuracy/Toy Accuracy: One of the eternal demands of the fans. Despite the divisiveness of the films, the toys are of an unbelievable high quality. This is especially surprising given the thousands of parts that make the movies' CG models, yet they were still able to create this Optimus Prime toy◊.
And then there's the Studio Series line. The premise of the entire line is to make new versions of characters from across the movie series, with particular attention to them being in scale with each other (as well as redesigning characters that had inaccurate toys due to an evolving character design with the movies). This resulted in characters like Blackout and Bonecrusher getting better toys than originally released.
Throw It In!: Michael Bay is a fan of playing around with the script. Shia was hired based on how well he could improv. Also, the reason Sam's friend Miles starts climbing a tree at the lake party is because the actor started doing it in between takes and Bay thought it was a goofy thing the character would do.
DOTM is introducing a "third" form for the Transformers, a battle-ready vehicle mode reminiscent of M.A.S.K.. The reason seems to be because Michael Bay saw the sub-line of the previous movie toy-line called "Stealth Force" that presented a very similar mode and liked the look. The Wreckers' NASCAR altmodes appear to have this form as their only vehicle mode (specifically, armored versions of the #42 of Juan Pablo Montoya, the #48 of Jimmie Johnson, and the #88 of Dale Earnhardt, Jr.).
Sam would've originally had the nickname of "Spike", and while the door was open for him to gain it in the sequels, it never happened. "Spike" does eventually get used in the fourth movie...as a nickname for Scorn, the Spino-Bot.
Soundwave was among the cast of the first film, but the production team couldn't agree on a way to portray him, so they left him for the sequel. Blackout, Barricade and Frenzy became Decomposite Character's, all serving roles Soundwave would've in one way or another.
Arcee was in the initial Autobot line-up, but was replaced by Ironhide when the writers felt it would take too much time to explain a female robot. The issue would go unaddressed in Revenge of the Fallen when she debuted there.
Princeton University was going to be named in Revenge of the Fallen as Sam's university, but Princeton refused to allow it after learning of the pot brownie scene.
The Fallen would've been sealed in a sarcophagus, something that made it into IDW fiction, but he ended up just sitting in the Nemesis in the film, something that shocked Chris Mowry (who took pains to write the complicated subplot). Also, Megatron was originally to deliver the global ultimatum, but it ended up going to The Fallen to give him more screen-time.
Optimus would've been Not Quite Dead, only in stasis lock after the forest battle.
Ransack, an ancient biplane Seeker was to briefly harass Jetfire before literally being Curbstomped to death.
A subplot regarding The Fallen falsely promising Megatron Primehood was dropped.
Sentinel Prime was originally Ultra Magnus; as a Development Gag, the design ILM fashioned for the Magnus character is the face that Buzz Aldrin and Neil Armstrong stumble upon (the one the dust collapses onto).
A scene where Sentinel observes the world's need for more playgrounds was cut, as was a meeting between Optimus and the President (the latter was likely cut to to the total likelihood of Obama filming a scene for a movie while, you know, leading the free world).
Mudflap and Skids would've returned only in a minor role, and then getting killed off, but due to the sheer critical backlash against them, Bay excised them from the film almost entirely (they can still be glimpsed in a brief scene at the NEST HQ).
Que/Wheeljack would've fallen into the Chicago river and have been killed by aquatic Decepticons. Similarly, Dino/Mirage was going to be killed by Starscream, and his corpse would've been used to taunt the hostage Autobots,
Megatron and Optimus would've explicitly teamed up against Sentinel, and killed him together with his own cosmic rust gun. Megatron, weary of the war, would've sincerely asked for a truce so he could leave to find and rebuild Cybertron, and Optimus would've allowed it. In the film proper, Megatron is less than sincere (still pointing a gun at Optimus and condescending him), and Optimus tears his head off.
A scene from Age of Extinction featuring Tessa dancing with Bumblebee and Hound was shown in the TV spot trailer but ultimately cut from the final film.
Lockdown would've had a poncho and a design more evocative of his Animated counterpart.
Concept art of Velociraptor, Apatosaurus, Stegosaurus, and Parasaurolophus Dinobots can be found. The Velociraptor, Slash, was intended to be featured in the film, while the Apatosaurus Slog and Stegosaurus Snarl were only featured in the toy line.
A silver-toned upgrade for Optimus was planned and heavily featured in the toy line but was ultimately cut.
A sixth film was planned and would've continued from the storyline in The Last Knight, but it was cancelled due to the film's poor performance and Hasbro ultimately deciding to retool Bumblebee from a prequel to a Continuity Reboot of the film series, thus ending the Bayformers series.
Peter Cullen reprises his role as Optimus Prime for the Michael Bay films, but he does not reprise his role as Ironhide. Frank Welker returns as the voices of Soundwave and Ravage, but his other characters (Megatron, Frenzy and Laserbeak) have new actors. He was going to portray Megatron once more, but Michael Bay decided that Welker's voice didn't match his vision for Megatron. Though he would get to voice Galvatron in AOE, and ultimately reclaimed the role of Megatron in TLK.
Amusingly, Frank Welker's brief lines for Shockwave in DOTM sound an awful lot like his G1 Megatron voice. Fans have also noted (often derisively) Soundwave sounding similar to Doctor Claw... which, amusingly is because Soundwave's voice is the same as Claw's; the vocoder effect from G1 was what made them different.
Working Title: Transformers Universe: Bumblebee first emerged as title, before reverting to simply Bumblebee.