Wow, that went sideways.
Again, really, for me, I've seen Marshall-Green in other television and film and this role is quite a departure. He's a solid performer, I see no problem with him. I frankly think part of the overblown response to the guy is the character, who is clearly brash, reckless and IMO condescending towards Shaw and certainly David, and that's who he is meant to be. And yeah, I roll my eyes at some of Holloway's foolish attitude like anyone else. But part of the reaction is, I feel, a knee-jerk response to the presence of a young, handsome man who ticks demographic boxes, which, I think, is seen by some as supposedly anathema in an Alien film.
I personally don't see it that way. Both Michael Biehn and Tom Skerritt were reasonably popular and attractive young, up and coming leading men when they played Hicks and Dallas, but it was not the form and function of their character. Neither is it so with Marshall-Green as Holloway. I think times have changed, looks have changed, style and film certainly, but I don't think that's what LMG's casting as Holloway was about. I suspect his stage work was seen and that's what got him the gig, because he's awfully good. I don't think it's a case of "how dare they cast a hunk in an Alien movie as a shameless attempt to curry the female demographic with this pretty boy" - I never remotely thought it was that.
Marshall-Green is playing what appears to be an arrogant, supremely self-assured egotist of a scientist. Everything about his performance and appearance - right down to the ascot, no doubt - is calculated to generate that. I'm sure Holloway is not a truly awful human being, but he leads with the arrogance. I personally find his and Shaw's relationship fascinating to ponder, because as I've said before, he seems to lead the charge, even as he's simultaneously putting her and her passion down ("I want to crush all man-made religions" - why?). I don't know why they're together, how they've related given his ego and her apparent demure shyness, and I want to. I can believe he loves her, but their dynamic seems thorny and imperfect - and interesting.
I have no further opinions on any of the other actors or their personal lives, except to say that Michael Fassbender may in fact be the finest leading man of our times and casting him was genius.