Don't worry there aren't any spoilers regarding the 22 minutes of the movie that were screened last night, but it does sound like we will not get a glimpse of whatever is terrorizing the town before the movie opens. Abrams made it a point to say that he doesn't want to show anything before the movie opens so despite what anyone has thought they've seen in the current trailers... it's not our creature.
Other than that, the guys over at Cinematical that caught the footage say that it looks great and if the rest of the movie plays like the short bits they saw, then we're in for a treat. You can head on over to Cinematical and read the rest of the post regarding the footage and like I said, there's no spoilers so no harm in checking it out.
Which brings me to another point, just like I did with Cloverfieldnews.com, there will be no spoiler talk in the comments. If I believe an item to be a spoiler for anyone that hasn't seen the movie I will remove the comment. Even after the movie releases in the US there will be no spoilers posted since there will still be places that the movie hasn't been released yet. So just keep that in mind. As the release date gets closer I'll setup a section in the forum dedicated to spoiler talk so that the people who have seen the movie can discuss what they thought without having to worry about ruining it for anyone.
Now if you want a slightly-spoiler filled review of the clip head on over to Shock Till You Drop and check it out. It still doesn't reveal a whole lot regarding the alien or plot points that we don't know about yet, but it goes into a bit of detail surrounding the train crash. Honestly though, after reading it I didn't feel that I ruined any bit of the movie for myself, although it does answer one question a few people had regarding the pickup truck that crashes into the train and who was driving...