Will Herondale is probably one of my most favorite characters. The way he battles his own demons may consider him as a complicated character but it adds more mystique to the story that I'm rooting Tessa to figure out what on earth went on with him. It pained me that he did grow old with Tessa unable to age, but I knew from the bottom of my heart that he had the greatest time of his life spending all of it with Tessa and their children.
When I first met him, he turned out to be more interesting than Jem. No offense to those who love Jem, but Will just impacted the story so much that his character was able to affect mine.
I connect with him on a personal level because I've been in his shoes before and because I knew what I felt like he portrayed. I'm not going to say it because if I did, my bedroom would've been flooded by the salty water pouring from my eyes. It's not hard to say "I like this character because he or she is so cool." He has been my number 1 favorite character, and I sympathize for Dorian because he's number 2, even as I reread the Infernal Devices and my heart still aches for him.
I don't know the reason why I felt this way the first time I read about him, but I guess it's always been that way. If I played Kiss, Marry, and Kill, and Will Herondale was included, I'd choose to marry Will. If Dorian had been included as well, then he would be kiss (I'm so sorry).
I'm going to stop from there because talking so much about Will reveals my fervent passion for the character. It might as well make me cry.