I really loved and hated the ending to Mary Stayed Out All Night: loved it because it provided a glimpse into what a great drama it could have been, a relatable portrayal of youth, love, and maturation; hated it because it provided a glimpse into what a great drama it could have been, a relatable portrayal of youth, love, and maturation.
Also loved the endings of Kim Sam Soon, Dream High, and 49 Days for just being pitch perfect.
I tend to hate endings that are all wrapped up with a bow tie and a wedding, but I'm going to add The Greatest Love to my favorite endings as well. I appreciated that just because it ended with a wedding, we still see that life for the couple isn't all rainbows and sunshine---the reality of being in the public eye precludes that, and good on the Hong Sisters for keep it real.