Everything about this film is done in excellent taste. The creature effects are vintage quality and extremely reminiscent of films like Critters or Gremlins, only a bit meaner. If there's any CGI work, it's hardly noticeable.
On another note, the comedy is subtle but always hits the mark. Fans of the Frost/Pegg movies will absolutely dig the unique quality of Attack The Block. Truthfully, during this one I felt the same type of surprise I felt when first viewing District 9.
The only complaint is the South London accents are so thick it's hard to understand at times. Plus, the characters speak at a break neck speed throughout. Subtitles may have served this movie well.