It's a sci if horror film. I don't watch many horror movies so I am not certain that I can compare it to anything. Initially most of the horror is psychological and in the minds of the characters, but the final 45 to an hour involves a more generic "we gotta save ourselves from the psychotic killer."
I liked it a lot; Sam Neill rocks. I was probably ~16 when I first saw it too, though it never disturbed me.
As for the video log... Hmm, spoiler tags have their own linebreaks, so my formatting got messed up trying to use the default tags. I opted to color the text that of the default background color; highlight such text to view it. Hopefully no one uses a non-default background color and gets spoiled unnecessarily. Note that spoilers are mostly such because of their grotesqueness, though they spoil the movie a little too.
The video you are referring to is basically the crew going ape shit insane and butchering themselves and their comrades in sheer terrified delirium. One particular segment that I remembered is someone either eating an arm whole or having their intestines pulled out through their throat . Given how smooth the skin appeared my interpretation favors the first. There is also a short segment at the end of the video when one of the crew members holds out two eyeballs his hand, and is (originally interpreted) as saying "save me from hell" in Latin. (This interpretation by the characters in the movie is incorrect, but you'll have to watch the movie to learn the correct interpretation.) I believe the video also pans to show the eyeballs belong to the individual speaking, a circumstance repeated later on by a character in the movie itself.