From Coming Soon:

Next up was Transformers: Age of Extinction, which was presented by Mark Wahlberg--Michael Bay was a last minute no-show this year--who also introduced his younger co-stars Nicola Peltz and Jack Reynor. Wahlberg talked briefly about joining the movie but also proclaimed that it was going to be "bigger and better than the other three combined" as well as the biggest movie of 2014. (Sorry, "Mockingjay"!)

Instead of just showing the most recent trailer, Bay had put together a good chunk of footage from the movie, maybe 12 to 15 minutes, similar to what he did with the original Transformers seven years ago. It gave us a much clearer picture of the characters and the general story while still leaving a good number of questions open.

The footage began with a shot of a dinosaur (very Tree of Life) and a bunch of sweeping establishing shots of mountains and fields as well as showing a sign saying "Remember Chicago" as homage to those who died in the battle of Chicago from Transformers: Dark of the Moon. We then see a number of alien spaceships invading a city and a battle between them and the Autobots, and then the footage cuts to a boat being boarded by a group of military men looking for something and Walhberg's character racing a jeep towards the scene. Stanley Tucci's character appears randomly and without any sort of introduction is complaining about the decision to hide in a glass room.

After those seemingly rather random scenes, the exhibitors in attendance were shown a nice chunk of footage from the opening of the movie, setting up the three main characters played by Wahlberg, Peltz and Reynor as the former's character Cade Yeager is bringing an old beaten-up truck back to the farm where he's greeted by Wahlberg's daughter Tessa (Nicola Peltz) and his partner Lucas (T.J. Miller) and they immediately get into an argument about him buying the truck, because money has clearly been tight for the Yeagers in recent years. But not quite as tight as Tessa's shorts, and this being Michael Bay, we do get a lot of gratuitous ass shots showing them off. Cade hopes that he can "flip" the truck for parts and sell it off, but a short while later, when he gives the truck some juice, we hear the unmistakable voice of Optimus Prime saying "Calling All Autobots."

We then see four SUV's holding federal agents driving through the fields towards the Yeager farm and in the lead is James Savoy, a tough agent who confronts Cade and the others. He's told by Kelsey Grammer's character over an earpiece to "work on the girl" so he pushes Tessa over, but before they can get too far in getting information, Optimus busts out of the barn and says "Here I am" and starts firing at the agents as the entire place literally explodes as Cade tries to escape with Tessa and Lucas. They're saved by the arrival of some sort of dune buggy being driven by Reynor's character Shane, who we learn (at the same time as Tessa's dad) is her boyfriend.

From there, we cut to a point shortly after that as their escape attempt is halted in the middle of a vacant stretch of road by a battle between Optimus and Galvatron, who seems to be controlled by someone at the command of Stanley Tucci's character. The fight is pretty heated as the humans try to hide behind cars but then suddenly Optimus is hit square in the chest by a missile and he falls to the ground. We then see the giant spacecraft hovering over the fields and out comes the menacing Lockdown, whose face transformers into a rocket launcher that sends another missile to take Optimus down on top of the car in which Tessa is in. (Tucci in the control room tells the person controlling Galvatron to get him out of there.) Lockdown then motions to the larger spacecraft that releases a smaller ship (probably another Transformer) with which the robot merges, before approaching Galvatron and the car under which Tessa is trapped, dropping a net over both and scooping them up. Cade and Shane run over to save her, Wahlberg doing an impressive leap into the air to grab onto the net before falling back to the ground once it gets too high.

These scenes were followed by a couple of bursts of footage, some from the earlier trailer and Super Bowl spot but also including more of Lockdown's giant spacecraft hovering over the city, a brief bit from a fight between Optimus Prime and Grimlock as well as Savoy chasing Cade across the fire escapes of Hong Kong. Throughout the footage, we see quite a few glimpses of Stanley Tucci and Kelsey Grammer's characters, as they seem to be playing the government types who have declared that the "Age of Transformers is over."

The footage ended with a funny scene of Wahlberg in a piece of a spaceship crashing down into a street and a guy in the car that gets damaged by the crash comes out and yelling at him about insurance. Wahlberg completely goes off on him, even heading back into the wreckage to look for an alien gun to shoot him with.

The amount of footage shown was quite overwhelming, but it succeeded on quite a few levels, firstly in establishing the relationship between Wahlberg as an overprotective father to Peltz's teen daughter. Showing this particular footage shows that Bay is going back to the basics of the original Transformers and making sure to focus on establishing the humans before getting too far into the world of battling robots. The footage also showed off a number of impressive set pieces that should be on par with the previous movies including one where Wahlberg, Reynor and Bumblebee are hanging from large swinging power cables that are draped over a tall building.

TLDR: Galvatron is NOT Megatron, but a human controlled and created Transformer using technology taken from studying Megatron's head/corpse(which has been seen on sets during filming).