To be completely honest...
I'm actually not very keen on this episode. The main reason is because, like you said, it was very serious. I think maybe there could have been a few comical things added in there, but whatever.
Then there are a few other things like the fact that it almost scared me to think that they were split apart (even though I knew they couldn't be forever.), and the fact that it almost made me cry (the final one almost did, but not in a bad way)
But other than that, I really loved the episode. The animation was crisp and clean, and the story is top notch. I really hope you make more, to!
All in all, great job!