The movie plays about with a number of the classic conventions of Alice, but adds in little details like Alice's clothes neither growing nor shrinking with her. The March Hare is highly amusing, and Stephen Fry's Cheshire Cat is, in a word, delicious, for all that his part seems small in the film.
Johnny Depp as the Mad Hatter, unsurprisingly, is a role with significantly more depth than I'd have imagined for the character, which is carried off phenomenally. Changes in the Hatter's mood are marked by his shifting accent, anywhere from a proper British Received Pronunciation with a slight lisp to a booming Scottish accent that makes Braveheart look mild. I've honestly never read the books (though I now plan to do so as soon as I have time) so I have no idea how focal the Hatter is in the original work, but Burton found a way to do so that makes sense.
Helena Bonham Carter's Red Queen shifts pronunciations and personality traits slightly as well throughout the film, and again in ways that make sense and have a definite pattern if you know what you're seeing. The contrast with Anne Hathaway's White Queen is very direct, and I'll tell you now that the previews did not do the White Queen justice. For the Queens, this is all a very elaborate game, with strict rules that must be followed by both parties.
In all, the movie manages to capture a level of whimsy with that delightful dark twist that was the way of faery tales before the Victorian Era got hold of them. Add into that the excellent casting, going beyond our main players to include Timothy Spall, Matt Lucas, Crispin Glover, Alan Rickman, Martin Csokas, Christopher Lee, and Lindsay Duncan (who played Adelaide Brooke in Doctor Who: The Waters of Mars) in supporting roles, and you've got a truly well-constructed adventure. Finally, I'll say that I've never seen Mia Wasikowska's previous work, but after her performance as Alice, the hunt begins.
I'd give more details, but it would really ruin the surprises...