Believe it or not I really enjoy the length of this game. I do agree that a shorter game might be more 'enjoyable' but I like the concept of being tortured I guess lol, as if I were really descending into a tunnel to hell. I think this game captures that feeling very well. That is to say I think I enjoy this game as more of an 'experience' than a traditional game. Like the dread you feel when you know you have 5 hours left in your road trip.
That being said, I feel like I wish the monster was scarier somehow... or like more of a looming threat than one you could see? The 'structure' of the monster also felt kind of claude coded idk but that could be a side effect of how it functions?