Jess, I have this habit that instead of listing what I like, I describe what I like and why, and how it works, then list a couple of examples. It may or may not help, but it's how I think and I hope it's useful.
What I like about magic in fantasy
After some reflection I've decided that I like magic that's unpredictable yet makes sense, evokes the morality and themes of the story, enhances the mood of the setting, increases the tension of the story and symbolises an issue that I care about in real life. It might be worth unpacking these a bit.
Unpredictable: The 'laws' governing magic aren't knowable or guessable to the reader, or the application of these laws is at least surprising
Makes sense: There's a deep, consistent sense of consequence that emerges as we read it - but which isn't necessarily apparent right away.
Morality and themes: The magic links closely to the choices that major characters make; their reasons for making those choices; the consequences that they encounter and my sense of whether those consequences are appropriately or inappropriately successful or unsuccessful, good or bad.
Mood: Self-explanatory. Magic evokes the world, just as setting does.
Increases tension: I like magic that makes things harder, not easier, on characters
Symbolises things I care about: I like it when the imagery of magic reflects stuff in my own life that I care about. This links to morality and themes. So, I like magic that somehow changes people, or holds up a mirror on knotty personal or social problems, or provides reflection on situations I can identify with.
The two earliest examples I found of magic that I liked were Madeleine L'Engle's A Wrinkle in Time, closely followed by Ursula Le Guin's A Wizard of Earthsea. To these I would later quickly add CS Lewis' The Lion, the Witch and the Wardrobe and eventually Tolkien's The Hobbit. Each offered outstanding examples of the above qualities. But there have been a lot of stories with magic that I don't wholeheartedly like too. But a few remarks about these.
Unpredictability: Stories can feature very orderly magic or very chaotic magic. A Wrinkle in Time has very chaotic magic, while A Wizard of Earthsea has very orderly magic. Really, the quality of unpredictability is a story-telling quality, rather than a story-design quality. Le Guin explains her laws of magic early, but then surprises readers with how they apply. L'Engle simply keeps readers guessing by throwing new sorts of magic in every other chapter.
Makes sense: It's not hard or uncommon to provide glib justifications for deus ex machina plot devices delivered via magic. The mark of good magical design to me is that the consequences seem in retrospect to be the only reasonable ones. This is especially noticable in both Lewis' and Le Guin's stories - perhaps because their magic has such a strong moral dimension.
Morality and themes: In each story I mention, magic is used to symbolise some element of human existence or desire. In each case, these elements are put into conflict. In each case, the conflict includes a magical resolution that also offers commentary on the social, psychological or moral.
Mood:The magic in each story is unique to that world, and captures the feel of place perfectly.
Tension:All the characters who encounter magic in these stories don't get an easy ride from it. There's always dilemma and sacrifice.
Symbolism:In each story I mention, the imagery isn't chosen for the degree of flash, but for its degree of symbolism in terms of theme, and its addition to mood. This is visible in (say) the Turkish delight in Lewis' story, or the gold encrusting the dragon's body in Tolkien's, the Jungian shadow-monster in Le Guin's or the links between mathemagic and love in L'Engle's.
There have been many other writers since who've impressed me in this way. Tim Powers was mentioned, and I agree. I'd add some of Gene Wolfe's writing too. Zelazny at his best does this too. (The magic in Lord of Light worked for me; the magic in the Amber series did not)
Many other fantasy writers are impressive for other reasons, but their magic often is not. Very often it's punctuation or gratuitous special effects or mood without significance or deus ex machina plot resolution -- all of which irritate me greatly.
Hope there may be some use in this.
