It's not easy warming up to a group of characters who spend the opening minutes of a film mugging with machismo and a switchblade a young nurse on her way home from work, but that's essentially what recent British sci-fi import "Attack the Block" is hoping you'll be able to do.

Written and directed by Joe Cornish, a heretofore British television comedian and longtime friend and collaborator of Edgar Wright (director of "Shaun of the Dead" and "Scott Pilgrim vs. The World," among others), the movie pits a gang of bike-pedaling youths against a dark tide of predatory alien invaders who descend on the rather mean streets of London one night under the cover of a citywide fireworks display. Between the ages of around 12 and 15, and led by the rather unsubtly named heavy Moses (John Boyega), the boys go at the aliens with fireworks, baseball bats, ice skates and at least one katana and quip like the kids from "The Sandlot" if their mouths were filled with profanity and South London slang instead of Big Chief chew.

Sometimes charming, sometimes redeemable, the gang is at the heart of a film that picks some of the choicest bits of monster, horror and sci-fi and melts them into a jaunty 90 minutes that's a refreshing entry in the tired and failing alien-invasion genre. The success of the film rests on the shoulders of the likability of its characters and the quality of its monsters, the former of which fails the most frequently. When the movie makes a point to try to turn its anti-heroes into heroes proper, there's the feeling that it's more their aggressive, territorial personalities that were the neat fit for fighting back the extraterrestrial invasion rather than it being a fight with some aliens that turned them into the virtuous saviors of their community.

"Attack the Block" deftly avoids making an apology for the young hooded toughs at its center, something that would have come off as unavoidably heavy-handed as it would have soured the summertime theatrical romp that the movie strives to achieve. The film neither moralizes the characters' actions nor ignores the social situation from which they arose, and while memories of the very recent riots in London are a bit like the kid in the theater who won't stop kicking the back of your seat, there's really not a lot in "Attack the Block" that's directly relatable to the events—aside from the fact that London has a bit of a youth violence problem and that, in the meantime, it appears as though they've got a pretty handy first line of defense against hungry invaders from outer space.

For having a relatively low budget, the film is handy with its special effects, and it has some great set-pieces of kids versus the aliens or kids running for dear life from the aliens that hold up until near the very end. The young actors are exceptional, giving standout performances that really give life to their parts even if the individual roles are rather thin. Jodie Whittaker plays the nurse who is mugged at the film's beginning and later finds herself in the somewhat believability-straining position of being the youths' ally and friend and Nick Frost, frequent opposite to Simon Pegg ("Shaun of the Dead," "Hot Fuzz," "Paul"), pops up as the wastoid stoner upstairs who's good for some easy if uninspired laughs. But it's the younger stars that are the film's focus and who carry the momentum from scene to scene. Young John Boyega has a stellar starring debut even when it is his character that is the hardest to get to like and the most difficult to accept on a podium by the film's end.

It's easy to root for the gang of youths as their misadventures bring down a host of nasty otherworldly beasts but never quite as effortless to like them the whole way through. The biggest hiccup here was the realization that nothing that happened over the course of the movie really took away the impression that Moses, the youths' gang leader, was not still headed inexorably toward becoming another Hi-Hatz, the slightly older, far less well-humored and exponentially more vicious drug dealer who shares the block with the central characters and provides to the film a human antagonist alongside the faceless police and the alien menace. On the whole, the film will be sure to find a happy home with fans of sci-fi and monster flicks despite its character flaws, and it sets a solid precedent for future works as the directorial debut director for Joe Cornish.

"Attack the Block" is currently playing at the Ann Arbor State Theater and is due out on DVD and Blu-ray October 25th.