I think it was well balanced, not a "good end" per se but a heartfelt one. I mean, humanity apparently is in fact gone, and Shin never will get to meet his creators and scientist friends again as promised. That is kind of sad, but on the other hand new things have arisen in turn and humanity's final efforts did bloom into something in the end. And while he'll never truly complete his mission, it's a real bright bit that he wasn't "compelled" to do so either and they left him freedom there to make a different choice when the circumstances changed.good ending