I was a bit hesitant to read this one. I only mildly like the first one (The Magicians), but didn't want more Narnia/Potter mash up. It turns out the second one feels a bit more original and, to me, more enjoyable. 
 There are two main plot lines and the story appears to lack focus, but once you get 3/4 of the way through everything snaps together and you realize that there was a purpose to all the meandering and even the smallest things become important. Also, the story becomes really interesting at that point and I could barely set it down. 
 In terms of characters, we get to see more of Quentin and he sounds a bit more mature than in the prior book, eventually even becoming a likeable character (I didn't connect with him in book 1). Julia is now a prominent character and her story arc is very interesting. She never feels as real as Quentin, though, so I wasn't as invested in her story. 
 The main plot is Quentin's quest, which starts of with him just wanting some adventure, but then actually evolves into a quest to save magic from its true owners- some cool stuff happens near the end. It left me wanting to read book 3 (there's a book 3 coming out, right?). 
 Overall: it was a good book. I can't quite pin point why I didn't enjoy it more or why I enjoyed so much. I'm sure you'll find something in it to entertain you, though.