It's a teen movie and it has claws, though they're largely retracted in the film's closing stretch - Heathers it ain't, but one thing that Mean Girls does well is temper the more saccharine, formulaic tendencies of its genre with a pretty sharp satirical edge (evident from the title, if from nothing else).
It's a cure premise - Cady Heron (Lindsay Lohan), home schooled all her life and having spent the last several years in Africa with her zoologist parents, starts at a public school for the first time in her life and becomes entangled with the ruling girl clique, 'the plastics'...cue many analogies between the law of the jungle and schoolyard practices (including amusing fantasy sequences of students acting out animal kingdom jungle behaviour) and some impressively mean behaviour all round. Lohan, who I haven't seen before, is good (and reminded me of someone I know who I suppose I shouldn't name), as is the rest of the ensemble (special mention to the long-suffering maths teacher, Tina Fey (who actually wrote the screenplay); also, Lacey Chabert has grown up and is completely unrecognisable; and, of course, Amy Poehler is always welcome). Liked it.