Just finished it. Didn't expect the ending, but loved it.

It was... a gut-punch to my soul.

I tend to agree with Keanu on the decisions made by the Fireflies and just how quickly they were able to jump to the conclusion of sacrificing Ellie. Unless Joel was out for weeks, it's highly unlikely they were able to try every alternative to creating a vaccine.

My biggest problem comes from the fact that an outbreak has occurred 20 years prior, leaving less than 40% of the world's population scattered across the globe, and a small, tattered revolutionary group thinks they have the resources, abilities, and coordination to create and distribute a vaccine by killing a young girl. The vaccine isn't guaranteed to work. Marlene even stated that she and her men barely made it to Salt Lake City.

The ending does create some fascinating viewpoints due to it's morally ambiguous nature. Joel is clearly not a hero though, in any way.