What's cool is that it defies all conventions and lets you decide what it is about. And proves that the guy who played Xandar can actually act.
The set up is simple. A bunch of friends hold a dinner party the night a comet is supposed to be visible in the sky.
One interpretation of the film could be that they simply have their dinner party and get too wasted and will wake up fine, but hungover, the next morning.
One interpretation of the film is that something really, really horrible and scary happened.
Another would be that something quirky and magical happened, but it's not a huge deal.
And I can see arguments for all three ways of looking at the film. (And I'm sure there are more possible interpretations I haven't thought of.)
It is a total nerd film. If you want an action film, or a traditional horror film or even a traditional sci-fi film, it's not for you.
But, if you want something that might simply make you laugh or might scare the living shit out of you, its a winner.
(I'm leaning towards the idea that the horrible, horrible super scary thing happened.)