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.
Even Better Sequel / Sequel Itis: Or remake, rather. Slender: The Arrival has been shown to do functionally everything better than its predecessor. On the other hand, the plot has been criticized as too vague and the length is said to be a bit too short.
That One Level: The abandoned mine area, where you have to turn on the generators seem frustrating to some since not only is Slenderman trying to get you but also his proxy who tries to chase you down and if it catches you, it cripples you making it a lot harder to get away later. Fortunately you can switch the modes on your flashlight to stun it, but the game doesn't tell you that. Heck even after you turn on all the generators, it can still get you while you're waiting for the elevator to rise.
What an Idiot: Seriously, Kate. If you have a something like the Slenderman haunting you, what makes you think that leaving your doors and windows open at night during a thunderstorm was a good idea? Granted doors wouldn't even slow him down, but that still doesn't justify being so slack with home security.
You don't need to be followed by Slenderman for keeping your front and back doors shut to be a necessity. Apparently, Kate's not concerned about her house being broken into.
It's also likely that continued exposure to Slender Man was already turning her into a proxy by that point. In which case, she may have taken a page from Alex, Jay, and Tim's book by leaving her camera on to discover what's happening while she sleeps. She may have seen herself be controlled into doing it. This may at least partially explain why she's filming herself in the video that Lauren finds.
Who lets their only child wander a dark, creepy forest that's known for disappearances? Essentially the entirety of the Matheson family's Slender Man problems were caused by them themselves, though, considering that one picture, it's entirely likely Charlie would have disappeared anyway. Just... later.