Paranormal Activity (2007)

Poltergeist for the modern age. A young couple discovers a nocturnal presence in their home and decides to capture the footage for themselves to figure out what's going on. At times, it feels like we're watching a really weird sex tape, but the money shot only comes when we shit our pants.

I remember watching this in a packed movie house in 2009, and it was one of the most memorable moviegoing experiences of my life. It sparked a major phenomenon at the time, including six sequels (to date) and a wake of shitty knock-offs that continue to this day. Often imitated, but never equaled; none of them ever came close to establishing the terror that had already been captured the first time. Not unlike The Blair Witch Project, it's usually cited as one of the best examples of the found footage genre because it manages to elevate the form through the simplicity of its storytelling. There's a reason why this movie was so successful, and that's because it's actually scary. Watching the security footage play out is legitimately unnerving as we scan every inch of the frame for what's lurking just outside the edges. One can claim that not a lot happens in this movie, but if you're invested, your brain does half the work. 

3½ shut the fucking door! out of 5

Note: I recommend seeking out the original/alternate endings if you're a completist, although the standard theatrical ending (as suggested by Spielberg himself) is arguably the best.