I think that, by the tone of many of the reviews, here, most people set themselves up for unrealistic expectations. It's hard to describe without revealing spoilers, but this is not your typical American "Happy Ending" type of movie.
Space is an inhumane and unforgiving maelstrom of forces that are bent on carrying forth cosmic agendas, cold and unfathomable to our insignificant human desires and pursuits. Best laid plans of mice and... something else. This is one of the very reasons I appreciate "hard science fiction" above all. It is the story of the most brutal conflict: man versus nature. It is the story of survival in a tired and cliched mass medium of man-versus-man car chases, sexual provocation, and predictable plot devices. It stands out.
Stowaway adapts a contemporary narrative based upon a short story called "The Cold Equations" from 1954. Undoubtedly worth reading, as well. This film casts a crew with believable emotions. Dynamic characters who make mortal sacrifices, yet the viewer can see the internal struggle etched upon their faces and actions at every turn.
The early plot and circumstance are mildly inconsequential as the story unfolds into an epic fight for survival. Those who dwell on "suspending disbelief" are missing the point: "Here we are, in this wretched situation, and these are the choices we made against the mounting pressure of inevitability."
This human experience shows what we are truly capable of when faced with unthinkable choices, which is the point of the original short story--a theme that Stowaway respects well, despite some easily overlooked, superficial details. I say: we are not watching Cosmos or some documentary on the History channel, though I wouldn't be surprised to see this work used as a case study for training real-life emotional resilience or ethics in the face of the most hostile environments imaginable.
Tough choices require the most stalwart minds and potentially the greatest sacrifice. Even if it all comes down to some cold, unforgiving calculation. You cannot argue with math, and likewise: you cannot argue with the tough moral dilemma faced by the crew of this mission.
Sometimes there is no correct answer, and Stowaway will not be celebrated for showing the uncomfortable side of making tough choices. But it should be. I commend the cast for being the messengers. But I do beg: please do not shoot the messenger.
To those looking for a more full human experience than the cliched American movie experience, rote with predictable high action, hackneyed sexual tension, and unrealistic car chases, I implore you to challenge the limits of YOUR emotional capacity by watching this underrated film. Ask yourself: what would you have done? Thank you for taking the time to consider my perspective.