I'm in two minds about the Black Goo
I like it, because I find the concept creepy as f**k' and even more disturbing than the Xenomorph. It'd rather have a quick head bite or even a 10 seconds stomach ache that a chestburster would give. I don't want to be suffering for days like Holloway did or even go through the horrific mutations Fifield did ( being still alive, but not 'you' anymore, and seemingly in terrible pain )
It also opened up a LOT of possibilities for the Alien universe for new and different concepts and monsters.
I dislike it because it somewhat ruined the image I had of what the Alien is and represents. As many have said, some mysteries are better left being mysteries, they stay fresh that way.
Similary with other horror icons like Michael Myers, once you explain away the ambiguity of his Evil by " A cult placed a curse on him when he was young " 6 movies in, it ruins it for me.
I feel similar to the Joker. What drives such a mind to do what he does? Is it mere insanity? Is pure Evil? Nope, just an acid bath that messed up some of his internal wiring.
I had no trouble with it during Prometheus as it was still left unexplained as to whether the Goo came from the Alien ( who they may have worshiped, thanks to the hints of the mural ) or vice versa. I mean we all came from goo didn't we? Surely the Xenomorphs didn't pop up out of nowhere. Perhaps the Engineers reverse-engineered a Xeno and found out where they from.
Now with Covenant and Ridley's comfirmation with interviews we know the Goo is an Engineer invention and the Alien is just a by-product of it, with a little of David's tinkering.
I don't like the idea of by the time The Nostromo reaches the Derelict, the Alien is only a mere 60 years old. Instead of a possible thousand, or even long before life started developing on Earth.
So yeah, I can appreciate the ups and complains about the downs.