I think the reason the recognisable aliens were ditched is that Ridley Scott didn’t want to re-tread the previous movies. Which in a lot of ways is true – it would have. Which begs the question – why make the movie at all? From what you’re saying they have literally taken an Alien movie and ripped the aliens out of it – that cannot ever really be expected to work.

In terms of the huge numbers of inconsistencies and peculiarities of the plot, I think it just shows the difficulty of making an ambitious movie – clearly some of the problems really could have been solved quite simply, and often in seconds. But the clarity of thinking required to do that clearly wasn’t available at the time.