The aliens were horribly weak... Oh, wait... (spoilers)
A pack of gang banging kids takes out a race of feral baboon invaders? And NONE of them even gets horribly injured? Where's the tension in that?
F-ing cheese fest Shakma (1990) had higher tension and was more terrifying than one second of this movie. Was (un)intentionally funnier and heartfelt too.
Oh wait... Well this piece of trivia from the trivia section sure explains it:
Writer/director Joe Cornish has stated that watching Signs and imagining what would happen if it took place in south London was an inspiration for Attack the Block.
What would have happened if Signs took place in the UK? IT WOULD START TO RAIN AND THEY WOULD ALL DIE OUT. THE END. How do you get inspired by one of the worst/most unintentionally hilarious alien invasion movies ever???