TRANSFORMERS 2007 Autobots and Decepticons fought for the engraved glasses to seek out the Allspark, it ended up killing Megatron thanks to a human boy. REVENGE OF THE FALLEN The Fallen wanted to activate the sun harvester to use the sun as Energon source, but he was too weak to do it all by himself. DARK OF THE MOON Sentinel Prime cut a deal with Decepticons to rebuild Cybertron, it backfired horribly because Cons are not to be trusted. AGE OF EXTINCTION Greedy corporation and government of Earth attempted to create an army of Transformers, and they unwittingly gave Megatron a new body. THE LAST KNIGHT Quintessa brought a fractured Cybertron back to Earth to drain its core, she must to be stopped because the Earth is actually Unicron. BUMBLEBEE The ballad of a girl and a giant robot that transforms in to a VW beetle. They saved the world from an invasion before their inevitable separation. Edit: It is all just personal observation on the storyline itself rather than about how good (or bad) these films are.