I'm a Bat-purist. I think Adam West should be used for a pinata. The only thing I respect about the original movies is the occasional intense look from Keaton, who I think is a great actor...but not a great Batman. Jack Nicholson acted just like...Jack Nicholson, not the tragic character who is the Joker. If you want a glimpse into that powerful, tempestuous mind, read Grant Morrison's Arkham Asylum. Or Alan Moore's The Killing Joke.
That being said, Christian Bale was Batman at his inception:
Gasser (?): I don't know, I swear to GOD!!
Batman: SWEAR TO ME!!!
This gave me cold chills.
I had to squint and turn sideways at Neeson's Ra's al Ghul. I always pictured Ra's as much more imperious. And they'd blasted well better have a Lazarus Pit lined up. (On a side note, if you ever come across Dtective Comics #400 (?) where Ra's dips himself alive in a Lazarus Pit and then proceeds to beat the stuffing out of Batman with his (Ra's) own broken hand, I'll give you a kidney in exchange.)
Gary Oldman makes Pat Hingle's Commisioner Gordon look like the stiff that played him in the 60's by comparison. The beleagured good cop in the midst of corruption fit him well...much like any role he assumes.
As for Ledger as the Joker, I'll give anyone the benefit of the doubt. Not that my humble opinion makes a bit of difference to Hollywood, but the Joker is more a force of nature than a two-dimensional character. Ledger's right, though...in the case of the Joker, you can laugh like Caesar Romero as long as a universe of pain reflected in your eyes.