It seems some ppl didn't like or understand why the movie went from a sci-fi thriller to a cheap horror movie with excess gore. Indeed, any movie that starts on a genre and turns to another will bother the audience that likes the initial genre and dislikes the later.

What I understood, is that the director wanted to take the sci-fi side to talk about space travel, wormhole, black hole and the sorts. But then when the ship does its thing, it ends up on another dimension where there's some kind of intelligent life forms, but the whole place is full of chaos and suffering and this sort of stuff. So the original crew members either embrace that vibe, or is tortured and killed, then some life form takes the ship as its body and goes back to lure more victims.

Some scenes are ambiguous if they're real or illusion, some are clearly illusion turned into a real place, and some are fully delusional as in a flashback. The life form that takes the ship is able to see ppl minds and learn their fears and then create illusions based on it. I don't remember any scene where somebody's fear is shown to somebody else, so I guess that it's unable to create any physical form. But it's able to take control of inanimate objects like the ship and of living beings like with Weir. It also seems that in doing so it's trying to persuade them into accepting the other dimension, which happened with Weir, but it can also control ppl and make them do stuff unwillingly until they recover control of themselves, as happened to that guy that tried to open the door and kill himself.

So, the movie does start talking about sci-fi stuff but then turns into a tough horror. The excessive gore takes part on it. We're never shown the actual other dimension, not even the life form that took the ship is shown. Everything from it is shown from visions and actions of crew members. The gore is the closest we see of what the dimension would be, representing stuff being destroyed and turned apart.

On a side note, the movie refers to it as chaos. In fact, on Science, chaos is a system that's unpredictable. It is so because any small change on the input or initial state leads to very big and varied changes on the output or final state. What the movie depicts is entropy, which represents organized forms becoming disorganized as time passes and in a way that's impossible to turn back. The sad thing is that our universe is ruled by entropy and we see it everywhere. It just happens too slowly on universe scale, and some processes like life create order instead of destroying it.