I can't get over how human Simon was. He apologised for his outbursts, even when punching the sub at one point, he repeatedly apologised for the radiation in the exact same way like he was still reeling from the shock of that information. Whenever the oxygen ticked down you can see a new wave of horror washing over him that he needs to take a second to cope with. When Ava gives him the login details he stumbles on remembering control-shift-9 never mind the password she rattled out.
They managed to present a man with a dark past and anger issues who is also not a monster. He is a human being desperate to survive and nobody even knows his name anymore. The closest thing he had to a family he resents but still obviously misses terribly as he clings to that pendant and shakes.
And Ava. Ava too. She's in an impossible situation. She doesn't want more humans to die. She has no idea how much damage radiation has done to her. This man, who she thought was a heartless killer, is begging and pleading and apologising like a child and it's getting increasingly harder to lie to him that he's going to be ok. Her screaming and begging that this is bigger than him is so achingly desperate I can still feel it, humanity is almost entirely gone. I fully believe that she hates this as well, all of it, but if she doesn't follow orders and take calculated risks then what else is there to keep her tethered and sane? What else can she cling to? They're almost entirely alone in an empty universe. She needs this hope.