These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Fridge Logic: How the tape was edited together and sent to the producer who is interviewed at the beginning is left unexplained.
He does state that there were over 70-something hours of footage, and what we see has been edited for time by his staff. Can't remember if he mentions how the tapes were found, though.
What's more interesting is that, if they edited it raw footage, why did they have archival footage of the hospital from 1942?
Genius Bonus: The Spooky Photographs Lance takes get progressively creepier. The first appears to show nothing, the second shows a blurry human-ish shape, while the third shows a screaming ghost on the other side of the window, hands pressed against the glass. Most people will only note the latter two pictures as creepy, but anyone reasonably familiar with ghost hunting shows (or just ghost hunting in general, really) will notice that the first photo contains a few orbs. As paranormal evidence, orbs are largely considered dubious at best, but a savvy viewer might notice them and expect further pictures to be more revealing.
Hell Is That Noise: A good number of spirits in the movie employ noises and screaming to creep out everyone, but abandon this at the halfway point and go full out attack.
The inhuman screams of the girl in the corner are downright horrifying.
Lance uses the voice detector device near the end and asks the building a question, in complete silence. When he plays it back, what he hears as a response sounds like hundreds of voices screaming and laughing maniacally. Random screaming and laughing can be heard with increasing frequency as the movie goes on. No wonder the characters become more and more uneasy... even if they can't consciously hear it, there were hundreds of voices around them all the time.
Narm: It looks like Houston dies from a ghost kicking him in the ass.
Grave Encounters 2 brings us floating cameras. It may be the work of the ghosts, but that doesn't stop it from looking silly. Same for the portal at the end.
For that matter, parts of the climax being filmed by the ghosts actually don't look at all like a Found Footage film, instead looking like a more mainstream movie. The contrast is surprisingly jarring.
Nausea Fuel: Lance killing and eating a rat, complete with gruesome closeup of him tucking into it. It gets worse in the sequel when he doesn't bother killing one before biting down.
Earlier on, the rotten food.
The Scrappy: T.C. for some. While his constant spouts of anger and frustration is understandable, the way he constantly gets on Houston's case and how he argues with everyone makes he unbearable at times.
And In-Universe, Houston himself grates on the others due to how optimistic he tries to be ("Maybe we took a wrong turn" or "Maybe an electromagnetic field made our clocks all go faster, so it's actually 6:30 instead of 8:30!").
Sequelitis: Though the first film is fairly well-received, the second film is far less liked, often being described as "incredibly far up its own ass".
Tear Jerker: Sasha crying for her mother towards the end. Grown woman or no, many of us would feel like doing the exact same thing after vomiting up blood.