Roughly, the basis for the poster I'd use (cover of the recent pop-up book):
I've already posted elsewhere
what I'd do,
pretty much. But I do know where I'd take the sequels:
2nd movie: The Obligatorily-Dark Second Act. Optimus Prime is arrested by Ultra Magnus and put on trial in an Autobot/Decepticon kangaroo court for supposed war crimes, just as Lazarus and his new movement decide to go into action for the greater good of humankind, using their misappropriated Cybertronian technology and a virus created from hacking into the remnants of Starscream's brain, with which they turn a few random Cybertronians into snarling savages in a Lazarus-staged effort to turn public opinion against the Autobots. But the virus gets out of control, infecting Autobot, Decepticon AND tech-outfitted human, after the defeat and general purge of the Sweeps in the first movie causes folks to gradually embrace technology again, enabling the virus to infect anyone who's so much as groovin' to their iPod, techno-zombify the occupancy of emergency response vehicles...and indeed even turn Lazarus' own self-styled "heroes" into murderous monsters in powered armor. The resulting nightmare forces Optimus, Magnus and Galvatron to team up in a standoff which ends with Optimus using the Matrix to purify the planet...at the cost of his own spark. (Basically a combination of Dreamwave's first two G1 arcs, with Starscream's Ghost and the Hate Plague from the cartoon combined into one concept)
3rd movie: Magnus is now the de facto commander of the Autobots, but his complete lack of experience with the now-hysterical human race only serves to get him blasted to near-death...a complication enough without a race of Gigeresque five-faced aliens called the Quintessons arriving on Earth promising to purge the Cybertronian influences on it in exchange for nothing more complex than a few archaeological resources. Despite their bizarre countenances, the Quints prove their weight in gold just enough to become media darlings even though Verity isn't entirely sold on this pretense. Which is just as well, as the situation crumbles even further when she discovers why exactly the Quints have REALLY come to Earth: to convert it into a cyberformed vessel for the limbo-entrapped spirit of their "Master", and turn the human race into techno-organic labor AND larder. With the Matrix now extinguished, Optimus dead, Magnus out of action, the Decepticons looking out only for themselves and humankind completely debilitated by global in-fighting in the face of Lazarus' imploded schemes, who can lead the Autobots in their darkest hour?
Here's a hint: he's yellow with black stripes... (Shades of G1's "The Key To Vector Sigma" and the '86 movie, with some of the more recent comic/cartoon plot threads worked in)