*Possible Soilers* Opinions. Take with a grain of salt.

I will list some of the things I learned about what hardcore Alien fans feel about "Alien Covenant" after watching the movie at the London premiere. I won't mention spoilers, but if you don't want to be conditioned by other people's opinions, just stop reading here.
Many say they are still "processing" what they have seen. However, there is a trend already. And apparently there is
going to be a lot of heated debate about the movie and the direction the franchise is taking.
I added a question mark to signal points that might or might not be accurate.

Positive things 
Visually stunning, attention to detail.
Well acted
Good characters
Return to horror
A lot to chew on
Gory
Better than Prometheus 

Neutral points
Several twists to the story, some of them predictable
Puzzling revelation about one character
Not enough connection with Prometheus (?)
It is David's story

Negative things 
Feels stuck between Alien, Aliens and Prometheus resulting in problems of tone
Feels like the writers did not watch the Original Alien
Like Prometheus, a lot of unanswered questions
Puzzling Alien creature behavior (?)
Excessively brisk pace, choppy editing as result of which the monsters barely register
Messy third act
Some will hate it, some will love it
Alien cannon shifts

There are no completely negative impressions from the bloggers, who acknowledge that the general audience may not have the same objections. However, some users (who I am assuming are also hardcore Alien fans) reacted very negatively to the implications of the criticism, leading to plenty of griping and fighting. All these seem to indicate that the press reviews are going to be pretty much mixed, with many of them being generous in consideration to Ridley Scott's status as a sci-fi innovator.

 *Spoiler Warning added by Svanya