I wouldn't say it's a bad film, however, it does miss the point a little. What made Alien and Aliens great were the atmosphere and the dread of the universe, the first two films made you scared to even walk out of your bedroom at night without any light around you or a torch in your possession, at least that is how I felt.
You don't get any of that with Romulus, you do, however, get a blast from the past to these films with the set design and in some ways the cinematography. The lead Actor Rain is just another version of Ripley which there is nothing wrong with that but it would have been better if you made it a relative of hers, maybe Amanda? She would have been an adult at this time as it's 20 years after Alien and about 37 years before Aliens.
My biggest ich about this film though is that it does somewhat rely on cheap jump scares and shock, which isn't what made Alien great in the first place and they should have concentrated more on the fear of the xenomorphs which also ties into my Atmosphere comment earlier.
The acting is pretty good, particularly from David Jonsson, who embraced the character and makes you believe that he is who he says he is, I did like the lead as well but not as much as David Jonsson, I would have liked Rain even more if she was her own character and not Ripley 2.0 the other actors did a good enough job but were a little overshadowed by David Jonsson, he was the shining light of the movie.
Alien Romulus will never be the best film in the series, I would say it is the third best behind Alien which in my own opinion is the second best and Aliens being the best.