Often in fantasy, magic is either arbitrary or stupid. It's either, let me put this plot point/metaphor in a bag that can only be awakened after these ridiculously specific things happen, or the magic in Eragon. Even Tolkien, who of course rocks, had pretty lame magic. I mean, really, a ring of power? Does it come with earrings? Maybe a nice broach, one that looks like a cat or something? But hobbits would look pretty stupid walking around with the super-boss heavy-metal belt buckle of power, encrusted with skulls and naked chicks and shit, so a ring it is.
The magic in Sabriel is not stupid at all. Internally consistent and well thought out, magic is something other than a deux ex machina. (It was in that moment that I felt the power flowing through me! I totally threw the bad guy across the room, he dropped the Evil Widget of Badness, and vanished from Eternia forever!)
The plot is a somewhat standard young woman comes into adulthood trajectory, but I thoroughly enjoyed going along. I enjoyed that the heroine wasn't you're usual gorgeous, brilliant outcast with a chip on her shoulder, but softer, more competent, more likely.