Season Finale Spoilers below:
Theyyyy'rreee Heeerrrreee! (Called that ending, btw!)
To me the most interesting part was the Littlefinger backstory. So not only was Robert's Rebellion built upon a lie, which many of us figured, but it was Littlefinger and Lysa Arryn that started the Stark/Lannister conflict, too.
I also love the conflict that was set up between Jon and Daenerys now, too. With Jon being the rightful heir (to both the Iron Throne AND the North) and well-liked, there's going to be some drama there. Granted, I don't think both Jon and Daenerys both end up surviving.
We also finally get to root for Jaime, too!