I love Neil Gaiman's American Gods.  The imagery is haunting, the characters are fascinating, and the idea is perfect.  The idea of exploring what happens when Old World gods come to the New World--and what new gods that world has--is not only a fascinating treatment of fantasy tropes, but also an insightful look into modern society.

It might seem strange that I'm gushing about Gaiman's novel in a review of Delia Sherman's Changeling and The Magic Mirror of the Mermaid Queen.  But in these books, Sherman explores similar questions--What do traditional characters from folklore look like in New York City?  What other magical creatures might live there?--in books geared toward a YA audience.  And just like Gaiman hit the nail on the head with American Gods, Sherman's novels are fantastic--not just for young adults, but for anyone.
Sherman's novels tell the story of Neef, a mortal changeling who is under the protection of the Genius (aka Head Magical Creature) of Central Park.  In both Changeling and The Magic Mirror of the Mermaid Queen, Neef ends up going on quests that take her all around New York City, giving her the opportunity to meet new people and expand her understanding of the magical world she inhabits.  Both of these novels are fun adventures, but it is the cast of characters that makes them truly come alive.  Thinking about what kind of mythical creatures would live on Broadway, at the MoMA, or in the fashion district is a lot of fun, and although I don't know New York City very well, I imagine that this aspect of Sherman's novels would be doubly appealing for someone who loves the city.

Sherman also does a great job of appealing to teens.  I remember back when I was a teen, one of the books I read over and over was Ellen Conford's Alfred G. Graebner Memorial High School Handbook of Rules and Regulations.  Each chapter started with a rule from the handbook, and then the events of the chapter showed some conflict with this rule, often to humorous ends.  Sheman's novels, particularly Magic Mirror, do something very similar--and it strikes me that this formula of presenting rules that exist, but can be broken, is one that is fairly standard in YA lit (hello, Harry Potter).  When presented like this, rules can be a safety net in case things get out of control, but they're not so limiting that they keep the protagonist (or the reader) from stretching her wings a bit.

Perhaps what I like most about Changeling and The Magic Mirror of the Mermaid Queen, though, is that they feature a female protagonist without making a big deal out of it.  Neef is resourceful, brave, and has good instincts--all features that make her a natural hero.  And she completes her quests without standing around saying, "Look at me!  I'm a girl who's a hero!"  Not only does this strategy make her a protagonist who will appeal to both guys and girls (this would be a great last-minute holiday gift for that teen who loves to read, by the way), but it demonstrates a helpful paradigm for including women in fantasy literature.  Female protagonists will only seem natural in fantasy literature when they behave as if their appearance there is as taken for granted as male protagonists--and Neef, with her self-assuredness, and Sherman, with her clear, engaging prose, do just that.