Wow. Wow wow wow. I was not expecting such a phenomenal story. I fell in love with every single character that Marissa Meyer wrote. I felt like I could personally connect with all of them. 
 So now I'm going to say something that does contain spoilers so don't read if you haven't read the book. 
 The reason my heart broke was because of that ending. No doubt like everyone else who read heartless. The death of that one character killed me. And let's get past the fact that this persons death JUST HAPPENED and to be honest I felt like it wasn't presented as well as it could've but either way, it still hurt. And let's talking about how this characters death literally killed everyone else as well. Catherine went mental. In my opinion it was her fault this person died and if she stopped for a minute and thought about everyone else this story wouldn't have ended so painfully. So Cath then became the Queen of Hearts and we all know who the Queen of Hearts is and how she treats people. Yea, so Cath went crazy. She became the psycho girl we all see in Alice in wonderland. She lost touch with all the people she once loved, and what she did to Hatte. That killed me the most. Hatte didn't want to go mad. And because of the thing Cath did, she changed him. She then went to his shop and her psycho behaviour towards Hatte hurt. She blamed him for everything and the one thing that Hatte didn't want to happen, happened. She made Hatte go mad. She is the reason he's known as the Mad Hatter. She basically ruined him. 
 So yeah. The ending sucked. Because someone died, Hatte went mad and Cath lost herself. Everyone broke. It was upsetting which is why I loved this story so much. I felt so emotionally connected with the characters that when they all lost themselves I felt like I lost a piece of me too.