At this point it's pretty clear they're setting this up as the grand finale of the Avengers so far, with the callbacks to the origin films, the focus on the original Avengers, and the title. It's going to be interesting seeing how they send them off.
That said, on to spoilery trailer stuff:
Spoiler
When the trailer moves to Hawkeye, it shows a clip of him teaching his daughter to shoot before going to current-day Clint, giving the strong impression he lost his family in the snap. Guessing he shows up on the radar months after the fact and Nat goes to bring him in.
There's a brief shot of Scott on a street seeing all the missing posters, suggesting he just got back from the quantum realm and has no idea what's going on.
They're not being coy about this bit any more: Tony Stark and Nebula make it to Earth. They're in the later shots of the Avengers in what people are apparently saying are "quantum suits". Also notable is that Thor, Captain Marvel, and Hulk are not shown - this could be significant since they are the three most powerful Avengers.
Thanos is also entirely absent from any of the trailers so far, so they're keeping his role in the story quiet. I wonder if Thor, Carol, and Bruce are off keeping him distracted while the others hop into the Quantum Realm to undo what he did.