With this third and final book in the series, we find a Quentin in exile, and a dying Fillory. 
 Despite getting a good portion of The Magician King to herself, Julia is almost entirely absent. I guess Grossman felt that her story was done, but it was disappointing. In many ways, her journey seems at least as important to the series as Quentin's - giving us the two paths of magic, the academic and the wild. I wanted more of her, I wanted to see her adventures on the other side (we're told that she's made queen of the dryads or some such, but I wanted to see that happening!). Instead, she's replaced with Plum, who was an interesting character, but who seems to just fall off Grossman's radar toward the end, and doesn't get nearly the amount of attention she deserved either. 
 Janet, on the other hand, gets quite a bit more weight. In the first and second books, she seemed rather hollow - a plot device with bitchy one-liners. While she doesn't get too much more in the third, she does get her own arc (narrated by herself after-the-fact, as with Julia), and she gets to have her own adventure. It's not much, but I enjoyed it, and it made her feel a little more real. 
 After turning into a niffin in the first book, Alice makes a comeback. I struggled with this. At first, I was worried that Grossman would just gloss over her experiences and she wouldn't get an arc of her own. But then she had such complicated and unexpected feelings about being saved, and that was great! And Quentin was caring for her and accepting responsibility for his part in what happened to her, and that was also great! And then they bone and that whole plot line just disappears. Nothing like the healing powers of sex magic, I guess? It was disappointing, and it didn't feel respectful to Alice as a character, and it didn't feel respectful to Alice as a person. And, suddenly, I had to wonder just how much Quentin really had learned. 
 Quentin's main foible has been his ennui - his inability to feel satisfied, no matter how amazing things are in his life. He's always messing a good situation up because he's too busy chasing a better situation. For the most part, he seems to have change - he's still clearly depressed, but he seems willing to make the best of things when he returns to Brakebills. He's not happy, but he does seem content to treat water for a while, which seems to be exactly what he needs. 
 Then he gets this opportunity to create his own land, and that seems to be a very direct test - did his growth take? Will it withstand a little temptation? And... I'd say mostly yes. He does still go ahead with his attempt to create a land, but it lacks the desperation of his previous choices. He seems to be doing it because it interests him, rather than because he needs to escape. That worked well, I felt. 
 All in all, the ending felt earned. There are things about the series that I don't like, and I didn't like them in Magician's Land either, but that's no surprise. But, overall, it worked.