Honestly at a loss to all the 1 star reviews, to say the least. I prefer to start any movie with default/neutral 5 and go from there, and have never dropped below 3 (for House of Fears, an utterly lifeless Halloween flick that somehow rates higher than this...)
I've seen plenty of Halloween-based flicks and this is definitely on the upper range, with most being passable 5s or slightly positive 6. I'd rate this 8 along with Rob Zombies Halloween (Carpenter original getting 10).
It is essentially torture porn as two girls enact a plan of torture kill revenge. Some of the scenes become quite uncomfortable, but I can't see this being any worse than Saw, which has a much higher rating? Granted their justification for such, revealed slowly throughout, is arguably weak compared to what is likely an overkill of revenge. In any event, it's just a movie, they were wronged but by varying degrees amongst their victims, and 2 years in jail didn't seem to help their state of mind.
The film is what it is, and it does what it does with a certain stylish quality. The performances were solid all around, there are some nice Halloween-styled visuals, and the quality of film and music were above average for most Halloween films (granted the more modern ones have all seemingly reached a rather consistent tone here).
If the trailer strikes your fancy, you'll probably enjoy it. Another review very apt in "Mean Girls meets Saw." Reminded me of a behind the scenes/inverted take on Scream or Scream 2 in which we follow instead the killers point of view of events. Strangely enough it also felt at times like an alternative "Ginger Snaps" sequel in which the two sisters have averted lycan encounters and matured their outcast duet into a Halloween murder house (the one looks very much like the dark haired sis, and the other is even Ginger-esque and more often is the one pushing their plans moral boundaries).