This may be heretical, but I did not like it at all.
I simply could not get past the main premise:
That a creature could hang around and wait for millions, perhaps billions of years intact for somebody to blunder into it.
I also did not like the minor premise:
That people are so goddamn stupid that they will refrain from shooting some stupid creature that is trying to eat them.
One more absurd premise was super-acid:
Acid. I have used the most powerful concentrated mineral acids (sulfuric, hydrochloric, nitric, chloric, and mixtures of them) and nothing in the Universe behaves like that magic stuff the monster put out. Furthermore, acid gets destroyed from reacting with corrodable stuff and quickly runs out of corrosivity.
Sorry to be a wet blanket.