Well it has some ideas...
Engineers are not elephant skeletons but humanoids genetically same as human race but apparently technologically more advanced. There is that f**king ampule room (with
head) which drove me to insanity during my search for all the clues on relief and murals... (there are many hidden clues that could very well have great impact on Covenant story!!!). We know that Engineers created humans (maybe following someones orders) and we have countless philosophical/mythological traces thrown in that movie.
Who is god? Thats a dangerous question. And maybe trying to find answers to dangerous questions (of creation/life/death/...) led to creation of abominations we cant imagine. Also the question of creation (Holloway said that there is nothing special in creation, anyone can create life!!!). And countles repetition of Paradise Lost/Prometheus/Lucifer/Adam and Eve/God motifs succeeded to impose trillions of great questions. I hope that they ll answer 2-3 major ones, and if they do, well, we ll have good movie.
What if Xenos are not mere bioweapons but assets in the story much grander than we can expect. We know that black goo and Xenos could serv as bioweapons, but for what, against who??? I myself would like movie that wants to lif the story to much greater level of storytelling... Such movies tend to be more scarry much creepier than those featuring a monster in a tin can killing numerous people.
Black goo (liquid of creation and destruction) is still a mystery to me.
I think that black goo isn't Engineers technology at all. They stole that like Prometheus stole the fire.