I will give it a rating of okay to pretty good. Nothing to rave about, but not bad. It was funny in parts, sweet, and given the plot... depressing.
Some parts did seem to drag, but that might just be my mood rather than the movie. I am still glad I watched it, even though I kept thinking about what I would do with my 21 days until the end of the world.
Now it's time to watch an episode or two of Modern Family, S2.