Gemini Man (now on Netflix) wasn't as bad as I expected. I was expecting total crap but it was meh.
The story is the usual "agent hunted by the agency". The premise of pitting the hero against his younger self feels dated, I remember catching a comment by Ang Lee that "only now we have the tech to do this film", but I would tell him this would have felt innovative back in the late 90s*, now it seems everybody does this sort of thing and you can still discern the CG anyway. The film actually seems often filmed against a green screen when there would be no need at all (like first restaurant scene), giving a very artificial feel overall.
Young Will Smith rendering is impressive... I guess they have loads of imagery to source from, but I would imagine if you shown to someone that didn't know Will Smith, they would be easily fooled*. Illusion breaks when he talks, still looks robotic/gamey in facial animations... but what they skimped on/didn't manage to sell is action stuff: the final effect is still very "CG Neo", action doesn't get that crazy so it's not as heavy on the eye as Black Panther or Neo, but people like us will notice it.
What I don't understand is why they used the CG character for some background animation: it's bad. When the clone is stalking the original he does stuff that would have appeared much better if performed by a free runner. And that reinforced my feeling that many scenes where on green screen for no reason, it feels they done it to ensure consistency when they had to insert the clone.
*I feel they basically put themselves in a lose-lose situation: by choosing a very famous actor (everybody will know the clone is fake) and because they couldn't do the CG any better than the competition... hence why it felt dated from the announcement.