This series has a really unique feel to it. It doesn't focus so much on political/cultural issues like many other fantasy novels, and the subject of royalty or romance is only given a bat of the eyelid in the grand scheme of the books. Instead, the main characters - their struggles, goals and fascinating personalities - and the unusual magic system are given a great deal of attention.
I rarely feel all that drawn to the main character, because they never seem interesting enough to warrant being the main character, especially when there are more interesting or sympathetic supporting characters. However, I absolutely adore Eli. He's entertaining, clever, and flawed. His flaws aren't glossed over, but when added to the appealing aspects of his character, you've got a person who's both complex and likeable. His POV's also deliver an aspect of wry humour and observation you don't often find in fantasy novels. This never detracts from the series themes of the books though, and Aaron had me almost in tears or clutching the books in anticipation as often as she had me laughing. Eli's relationship with Josef and Nico, and the strong themes of friendship in the books were also incredibly compelling. The other characters are also very unique, each distinct from each other, but equally fascinating. Even more minor characters like Sparrow and Tesset had me cheering for them and wanting to know more about their stories.
The magic system also feels very unique, with its individual spirits, demons and Powers. Despite the humour in the series, issues like Nico's demon and spirit enslavement all feel like gripping threats, and I found myself becoming very concerned for water, doors, things that in the real world are just things
. The spirits each have fascinating personalities, hierarchies, and the organisations that involve them (the Spirit Court and the League, namely) are excellent to read about.
I'd say it's one of my favourite series, and I can't wait to see what Aaron writes next if it's half as good as this.