Would have been better without the monster

I thought this movie kept it up in all the scenes where no monsters were present. I liked the opening scene, the part where they were trapped and had to find a way out, even the rat and the ale were ok, but the monster was way over the top and completely unnecessary. I mean: the movie had a great setting, a claustrophobic atmosphere, great scenery, adventure, a threat (being trapped and not found), someone getting sick, but the monster had no story to tell and made it look like a cheap popcorn movie. The monster was also way too skilled: it could climb, swim, dive, fly, drive them in a trap, see in the dark, hide between scorpions; for a cave creature!