I've written a longer review of The Ploughkeepsie Tapes for my website, The Midnight Selections, but I figured I'd also try a shorter review here.
What makes this film different than other serial killer flicks is that its killer remains enigma throughout. Nothing is done to humanize him and this makes the film feel a lot nastier than it really is. We learn so little about Ed that in the end, he still could be my, or your, neighbour. (except he is fictional)
The snuff film look helps add a slice of authenticity to the film, but the acting of the interviewees, which is still good, isn't up to the standard of the very best of the found footage genre. (On a side note, I am a bit disturbed by all the people who thought this mockumentary was real. Has The Blair Witch taught us nothing? Found footage horror is never real, but it will always claim to be...cause why not.) Still, I liked the F.B.I. interjections because it helped to provide some dark humour to the film.
The film itself is not particularly extreme; however, that is only because Dowdle knows when to tell and not show. Still, the film was considered extreme enough for MGM to shelve it for way too many years. So, yes, The Ploughkeepsie Tapes can hit a nerve or two. This one was made for those who already know they can stomach a lot. If you already know that is not you, your best to watch something else.