Wikipedia sums it up well: Attack The Block is a "2011 British science fiction comedy horror film written and directed by Joe Cornish".
ATB is about an alien invasion in a London ghetto and some kids who fight back against the invasion. Let's see, cross Home Alone, Aliens and New Jack City (or alternatively season 3 of The Wire) and you get ATB. ATB is an enjoyable movie because of: the cuteness of the kids fighting the aliens with their relatively cute paramilitary ways and the fusion of the English accent and ebonics. The film also has a clarity and a freshness to it which is impressive considering that it's not made by an established director, and does not appear to have big stars, a big budget and the plot is unusual.
Attack the Block has received widespread critical acclaim. It currently holds a 90% 'Certified Fresh' rating on Rotten Tomatoes and has a score of 75 out of 100 on Metacritic, indicating 'generally favorable reviews'. Scott Wampler of The Examiner rated it A+ and said it was officially the best film of the festival and likened it to other debuts such as Neil Blomkamp's District 9 and Quentin Tarantino's Reservoir Dogs. Matt Patches writing for Cinemablend said "Attack the Block, even on its small scale, may wind up as one of the best action movies of the year". IGN gave it four stars saying "Cornish directs with the confidence of a seasoned pro" and calling the film "a blast from start-to-finish." Ben Rawson-Jones of Digital Spy awarded the movie four stars, saying that it is "exactly the kind of distinctly homegrown product that the British film industry should be making". Mark Kermode gave a mixed review saying he did not dislike the film, but "wanted it to be funnier" and "needed it to be scarier". Upon its release in the United States, Attack the Block also received critical praise. In his positive review, Chicago Sun-Times critic Roger Ebert praised the film's use of character development and the performance given by John Boyega.
On its opening weekend in the UK, the film came 3rd in the box office garnering £1,133,859. In North American limited release, the film has grossed $1,012,223 (£659,040).
I enjoyed some of the lines in this movie like when Boyega says that "the feds" (the British police) introduced guns and drugs into the community, but they weren't killing off blacks fast enough so they decided to pick up the pace and introduce aliens. His white comrade replies "believe", which sets off some laughter. There's also some good banter like when the women they mugged is debating with them after they have broken into her home and they say she has a "potty mouth." The exchange is pretty funny.
There's a few things that are dubious or weak, such as parts of the final action scene and some questionable deaths in the film which reduce the good fun (a more entertaining and less sappy Home Alone factor) of the film, and which is why the film can also be called horror. The attempts at social commentary are half-hearted and seem a bit strained. However, on the whole I think that the strengths of the film, which have already been mentioned, make it a movie worth watching. It's fun.