I'm almost embarrassed, but it was Legend of Korra....The follow up series for Avatar the Last Airbender. I didn't think a cartoon would do this to me, but it was really THAT good. The kicker is that everything was neatly wrapped up and ended pretty much happily. They're even going to have another season, so it's not like it's even over. Part of me feels completely adrift, while the other part of me is agog at how overdramatic I'm being about this.