I thought Batman Begins was darker. This one is just another action romp, albeit a very good one. The Joker is evil to the bone. Too evil to be seriously dark.
A very enjoyable movie. Bloody loud though.

BTW, did anyone else see any Tom Waits in Heath Ledger's Joker? I wondered if he hadn't used Waits in the same way Johnny Depp used Keef Richard for Jack Sparrow.