Just to say it again: Spoiler alert.
So, first, an overview, with hardly any spoilers, and then for the obsessives, the nitty gritty. Paramount played about twenty minutes of footage, including the entire monster-freeing train crash. As with the trailer, the whole thing pretty much nails the vibe of the Spielberg alien movies set in the late '70s. The soundtrack, the light, the attention to period details (the kids in the movie communicate late at night with walkie talkies), the just-teenage angst, the kids-against-the-world vibe. Joel Courtney, the lead actor, with his big limpid eyes, even looks remarkably like E.T.'s Henry Thomas. Like the Spielberg movies, Super 8 seems as concerned with feelings as it does with aliens — it's as much a coming of age tale as a monster movie.
Only two quibbles: There's a gang of boys that all hang out and make movies together. In the grand spirit of the cliques in Stand By Me and The Goonies, they joke around and throw stuff at each other and are just beginning to talk about girls. They look great (not super hip, but gangly, with braces, like real teenagers) and their dialogue isn't overly clever, but it did feel a bit unnatural, the only part of the movie that was trying a little bit too hard to be like something else. The other quibble, which, given the "blow things up!" imperative of summer movies, some will hardly think is a quibble: The explosion of the train goes on nonsensically long, with so many cars flying through the air, it seems like it must have been miles long even though it doesn't look it. (To be fair, Abrams even said it was way too long when he was introducing the clip.) The length is particularly noticeable because huge fireballs were not a big part of the Spielberg movies Abrams is cribbing, and with everything but this explosion, Abrams is all insinuation (you don't see the monsters, you just see what they can do). It sort of feels like Michael Bay hijacked some frames. But, all in all, if you are tremendously excited about Super 8 keep on keeping on.
To the details: Those with lower spoiler thresholds are highly encouraged not to continue!
The movie is set right before summer vacation. The main character Joe, is a 14-year-old boy whose mother has recently died in a mill accident, and who doesn't have a great relationship with his father (Kyle Chandler), the town sheriff. Joe makes movies with his four other friends, under the direction of Charles, a chubby kid with a director's complex. The boys all sneak out in the middle of the night to go to shoot a zombie movie at the train depot, a place they can get to thanks to Alice (Elle Fanning), a 14-year-old who goes to school with them. She's agreed to appear in the movie, and has secretly borrowed her father's yellow muscle car to drive them to the depot. Joe has a big, moony-eyed crush on her. While they're rehearsing the movie, a train starts to come down the track, and Charles, excited about the potential production values, rushes everyone to film while the train is going by. As the train passes, Joe spots a pickup truck driving onto the track, and directly into the oncoming train. The train goes boom, the kids go running, the camera, still filming, falls to the ground. After a massive series of explosions seems to have finally stopped, the door flies off one of the train cars, and Joe hears something slip out. The kids, who have scattered, all find each other. There are hundreds of objects that, in the words of a character, look like white Rubik's Cubes scattered around, and Joe pockets one.
The kids see the pickup truck that drove into the train, all smashed up, with a man sprawled over the steering wheel. It's their biology teacher, Mr. Woodward (played by Mayor Royce). They go to touch him, and out of his hand falls a map of the United States, with the train's path and times written on it in red marker. Mr. Woodward wakes up, takes out a gun, and says "They will kill you, do not speak of this or you and your parents will die," and then brandishes the gun until the kids run off, grab their equipment, and drive away. Just then, a squadron of Air Force soldiers (led by Noah Emmerich) jogs onto the scene, and finds the boxes their film came in. The kids agree not to say anything, and Joe goes home to play with the white cube in the bath.
As for what the alien looks like: who knows! There is one flash in a later scene, of a gas station under attack, where you can maybe see the reflection of a monster in a puddle. It's wispy and ghost-like, floating above. The characters in the movie who actually lay eyes on this thing are much more freaked out than they would be by a ghost, so we can only assume when seen in something other than a puddle, it is much more intimidating.