In 7 words or less: Scary as hell, if you are invested.
Best bits? I've never had an experience of fear at the cinema quite like the final 5 minutes of this film. It actually had my heart beating and it continues to have the same (if not quite as strong) effect on me on each viewing. It's simply an awesome legend, the interviews at the beginning really set the scene for some absolutely real-feeling terror. Each time night comes things get worse and worse, those poor little buggers. Things are about to get even freakier too.
Did it make you think thoughts? I can't think of another horror film that splits audience opinion as much as this. As someone who absolutely loves this film, I watch it and want to be scared, I invest in the story and the legend and the film sweeps me away into terror-land. There are no jump-scares, very little gore, no sight of any monster, just the very real terror of the actors and your brain to make up the rest. For better or worse (probably worse) this film has influenced a generation of film makers and films.
Would you watch it again? Yes. Twice at the cinema on release and probably ten home watches. The ending gets me every time. On each watch, however, the arguing between the group can start to grate.
Rating (out of 100%): 92% Oh god. It's scary in the woods. This could be my favourite modern horror. I defy anyone to watch this on their own in a dark cottage in the woods and say it's not terrifying. (No tweeting or texting allowed. in fact, turn your bloody phone OFF! eg: '@bigDave watching blair witch, with the lights on, it's total crap man. Pringles are nice. just read your email. Monkies Lol #crapfilm')