I have one dedicated article for my appreciation for The Infernal Devices, but The Mortal Instruments universe was really my teenage fantasy series. It was also quite easy for that to be the case considering the sheer number of books Cassandra Clare has written.
Each series is YA fantasy and follows a group called Shadowhunters as they work to fight demons, and often other, more dangerous, more human threats. In the Shadow World are also Werewolves, Vampires, Fae, and Warlocks, with mundanes (normal humans) shown to be incredibly confused when they start to learn more about their world. And sometimes an angel might make an appearance.
1. The Infernal Devices
I rank The Infernal Devices first because it feels cohesive and timeless, especially since it takes place in Victorian England. Admittedly, it does have a weaker plot, but that is made up for with the incredible cast of characters. Each character is written in a way that makes them feel like three-dimensional, complex, sympathetic people (well, most of them). The third-person point-of-views of multiple characters build a deeper understanding and connection to their plights and development. All of these points work in tandem to explore a variety of themes regarding life, love, and self-discovery. The character-driven nature of this series makes the emotional investment much richer.
2. The Dark Artifices
Next, we have The Dark Artifices! This is a very solid balance between a character and a plot-driven story since the series is written in a way where they continue to influence each other. A bit darker and grittier, the series untangles this mystery that's very personal to many of the characters. Therefore, they continue to evolve, for better and worse, as they each learn and experience the harsh realities of the world around them. This ties into themes of justice and vengeance, ostracization for being different, complex attachments, family, and loss. The Dark Artifices equally keeps the audience hooked on the unraveling mysteries, and the effects they have on characters you grow to love and hate.
3. The Last Hours
As much as I love The Last Hours, it is ranked third because of the disappointing payoff. It has a similar dynamic to The Dark Artifices where the plot and characters feed one another, but to a lesser extent as the characters shine. Books 1 and 2 really develop our extended cast of characters, each with a unique personality and set of problems that they work through. We certainly see that each is flawed but has its stand-out moments of vulnerability. However, the third book underdelivered on the potential of what could've been by making decisions that felt convenient, out of character, or nonsensical. I still appreciate the thematic depth of the series, throughout all three books, emphasizing friendship, self-hatred, guilt, and growth.
4. The Mortal Instruments
The Mortal Instruments has some of my favorite characters (shout out Raphael Santiago), but it is ranked last for the sheer amount of what the books try to do. I tend to think of The Mortal Instruments two separate trilogies following the first three books, and the second three books. The positives of this series are: that the group of characters is interesting and dynamic, their relationships are both humorous and impactful, and the plot, at its best, is captivating. The downside of The Mortal Instruments is how convoluted it is: With two interconnected trilogies, there's just a lot happening; there are twists that can take the audience out of the story altogether and can become hard to look past. Some plot twists are messy, don't feel purposeful, and even detract from the story. This is also the only series with page-to-screen adaptions since it has a 2013 film and a 2016 show.
Bonus
To round out this article, I did want to mention that there are several short story collections in this universe. These include Tales from the Shadowhunter Academy, The Bane Chronicles, Ghosts of the Shadow Market, and Secrets of Blackthorn Hall.
The last series in the The Mortal Instruments universe, The Wicked Powers is set to release over the next few years.