Spoilers, okay? Tons of 'em. Like a metric fuck ton of spoilers for not only Guardians of the Galaxy, but the entire Marvel Cinematic Universe are coming your way so, if you want to avoid those, just watch the trailer a hundred times and ignore my words. If you're as jazzed as I am about the MCU, though, go ahead.
This is the first trailer we've seen for Guardians of the Galaxy. If you know what to pay attention to, it confirms a lot not just about the plot for this movie, but the direction that the rest of the MCU is going to take over the next few years. First, a little review:
At the end of the Avengers, we see The Other (the faceless being who liaises with Loki on behalf of the more sinister evil) appealing to his master. Speaking in reference to their failed battle against the alleged "meager might of earth", he says "To challenge them is to court death." At this, his master turns and smiles, and comic book nerds everywhere learn his identity:
Thanos of Titan.
At that point, nothing was confirmed, but we could speculate. By far, one of Thanos' most well-known stories is the Infinity Gauntlet. In this story, Thanos collects six Infinity Gems: the Time, Space, Soul, Reality, Power, and Mind gems. These six gems combine to give Thanos complete mastery over the entire universe. The titan then uses this power to woo his beloved: Mistress Death. To win the affection of the physical (and apparently female) embodiment of death, Thanos snaps his fingers and blinks half of the universe's life out of existence. Needless to say, this threat calls on a force much greater than just the Avengers to combat. Why does this story matter when all we got in the Avengers was a cheeky grin? Because Marvel has been building towards this plot line since the first Captain America.
Oh, and Guardians of the Galaxy is about to play a big role in telling that story.
The Tesseract featured heavily in both Captain America and the Avengers as an item of untold power, but nothing particularly special beyond that. After all, as Thor showed us, there are plenty of objects with immense power in the Marvel universe.
However, Thor: The Dark World features yet another object with unspeakable destructive ability. The Aether. The Dark Elf Christopher Eccleston attempts to use the Aether to plunge the nine realms into darkness. His plan is obviously thwarted as evidenced by the fact that your lights still work and our heroes collect the Aether for safekeeping.
In the post-credits scene for Thor: The Dark World, we get a metric ton of bombshells dropped on us at once. Sif and Volstagg bring the Aether to space Liberace (otherwise known as The Collector). When asked why they brought it to him, Volstagg replies that "The Tesseract is already in Asgard. It is not wise to keep two Infinity Stones so close together." The Collector agrees and accepts the responsibility of safekeeping. As the heroes leave, he says, "One down. Five to go."
In this one scene, we confirm a few very important details:
1.) The Tesseract is an Infinity Stone (Kevin Feige has separately confirmed that, specifically, it is the Space Stone).
2.) The Aether is the second Infinity Stone (separately confirmed to be the Power Stone).
3.) The Collector will play some role in bringing the six together.
Whether The Collector is actually a villain that will try to use the six stones is unclear (short version: this would be a rather large departure from his character in the comics). However, he does have certain gifts of foresight and whatever his motives are, it's easy to assume that he knows what's coming for the Infinity Stones.
He also appears in Guardians of the Galaxy. You can see him in the trailer below at 1:59.
If we knew nothing else about the overall plot of the MCU/Guardians of the Galaxy, this would be enough reason to be excited. Fortunately, we are not so limited.
What follows are spoilers for Guardians of the Galaxy. Everything up until this point can be be gleaned either from previous movies or the inevitable follow up searches. From here on out, however, you're in serious spoiler territory.
In the beginning of the trailer, we see Peter Jason Quill (aka Starlord) getting all Raiders of the Lost Ark with a grey orb. According to the official movie description, this orb has the potential to destroy the galaxy. Two villains, Ronan the Accuser and Nebula are pursuing the Guardians to steal the orb.
That orb is the third Infinity Stone.
It's unclear exactly which Infinity Stone it is (only Time, Soul, Reality, and Mind remain), however it has been independently confirmed in interviews that a third Infinity Stone will make an appearance.
Furthermore, Nebula, one of the two villains in pursuit of the orb, is (allegedly) the granddaughter of Thanos. You remember him from earlier, right? Big guy, cheeky grin, wants to bone Death? Yes, it's his (possible) granddaughter that's chasing down one (or more! Does she know The Collector has the Aether?) of the Infinity Stones.
The plot to the Guardians of the Galaxy movie probably won't involve Thanos taking over the entire universe. It might not even really touch on the broader Infinity plot at all. And lest you get over excited, the next Avengers movie already has a big-name villain (in case the title Avengers: Age of Ultron didn't give it away), and we've only seen three Infinity Stones anyway, so the likelihood of these connections being a central plot point to the Guardians movie is hovering somewhere between zero and none percent.
However, this is also the most direct connection we've seen yet to the one plot that's been tying all of the MCU movies together so far. Right now, the assumption is that Thanos may appear in Avengers 3, but even that's not a given. How long this plot gets drawn out is unclear. What is clear is that Marvel is taking its dear sweet time in building a truly epic plot for one of the most ambitious comic book stories ever put on film. And the Guardians of the Galaxy is going to be a huge part of that. Possibly more than any of the previous Marvel movies.
If you're wondering why this got made instead of the dozen other standalone films we all want to see, that's why.