Without saying too much spoilery stuff, its essentially a film about two guys (Pegg & his often co-star Nick Frost) who are travelling across the country & end up with an alien (voiced by Seth Rogen) that is trying to escape Area 51 as a passenger.
The film is rated "R" for sexual references & drug use. So perhaps keep your kids at home for this comedy.
One thing is certain, Simon Pegg (Hot Fuzz, Shaun Of The Dead, Star Trek, & currently filming- Mission Impossible 4) is proud of it & thinks you will love it.
I asked the Paul star to give me a few words on it, and he quite literally gave me a few words...but the few words he chose suggests "go see this movie". Sooooo, i will be doing so today, and with Mr. Pegg still in the city filming MI4 right now, maybe he might stop in and see it himself...even though hes probably had to sit through it multiple times already...but if its as good as he says, why wouldnt he?