I've already shared my love for the City of Bones, so now it's City of Ashes' turn. :) 
 This book definitely has more dark parts than City of Bones, and it's packed full of action. After the revelation at the end of City of Bones, which I'm sure anyone who's read knows what I'm talking about...Clary and her friends have even more challenges up ahead. 
 In City of Ashes, There is a transformation, more magic, more demons, a prison escape, and an authoritative figure hungry for vengeance. I'm trying not to give away anything to big from this book, but I'm hoping I've peaked your interest with those snippets right there. 
 I'm a huge Jace fan...if that wasn't already blatantly obvious from my review of the City of Bones, but boy does that boy go through some classic teenage angst here. His life is a never ending woah is me fest in here, but to be honest, homework seems easy and not worth complaining about compared to what he goes through. 
 We see tonnes more of Simon, which is always awesome...especially when Jace is also around. Jace and Simon together equals written gold, they're hilarious...and LEGEN....wait for it...DARY (note: yes I do watch How I Met Your Mother, how can you tell? :P). Simon definitely faces his own challenges in City of Ashes, and he grows a lot as a character...and I'm not talking about getting his first chest hair, although that might have happened, but we don't know about it if it did.... 
 Magnus Bane's role just gets bigger and bigger in this series, and honestly, I don't think anyone's complaining there. Magnus is an amazing character...even without all his magic and immortality, he'd still be awesome. He's definitely one of my favourite characters in the series, I mean how can you not love someone who is that obsessed with glitter?! 
 I don't want to say too much about Clary because she's kind of centred around the whole cliffhanger from City of Bones, but I will say that she definitely comes into her talents and skills in this one. I think Clary's an amazing character personally. I know some people think she's a weak heroine, but I think she's one of the strongest. She never gives up and waits for someone else to save her, and she's always trying to get involved with the action. Some might call her reckless, but I think she just thinks with her heart rather than her head sometimes, and I just can't fault someone for that. It's amazing to see a character who has that much love, and honestly, isn't that why we all loved Harry Potter so much? 
 We also meet a new character, Maia. I liked Maia, but again, I don't want to give too much away. She's biracial, and also a downworlder, so she kind of brings in other races, both from the Shadow World and from the ordinary everyday world. She's definitely a fierce character and you do not want to make her angry. 
 Izzy and Alec are also getting bigger and more definied as characters in City of Ashes. We get to know both of them a little better, and Izzy has one of my absolute favourite lines from this book. 
 Ok, so obviously, you can see that the characters are becoming more developed, which definitely made me grow more attached to the series. I absolutely loved City of Bones, and City of Ashes too. It has the whole forbidden thing going on, and it is an amazing action-packed story. In fact, I recommended and borrowed this series to one of my guy friends and he loved it....which was awesome because it finally gave me someone to talk about the series with. He liked Simon more than Jace though...go figure. :P 
 Anyways, I think that The Mortal Instruments series in general, is great for boys and girls. It's one of those series that seems to not have gender, sexual or racial boundaries...it doesn't have age restrictions either. I'm sure I'll still love this series years from now. Cassandra Clare has done an amazing job at making the series reachable to all. She has romance, action, and even religious tales woven within the story. One of the biggest things I love about this series are the quotes from Paradise Lost, Dante's Inferno and other classic works. I love how Cassie ties the quotes into the chapters and the different sections of the stories. They even inspired the series, and one day I'll finally read the classics...and maybe I'll finally catch all the references within the series.