Sean Collins’s entire review of The Dark Knight is worth reading, but I especially like this part:
Ledger’s Joker is a creature in that vein, but instead of being larger than life, he’s smaller than life. I know that seems counterintuitive given the for-the-ages performance he turned in–surely this will be the most-referenced portrayal of a Villain since Anthony Hopkins’s Hannibal Lecter–but what the Joker is is a human being reduced to only cruelty and glee.
Nicely put.