One of the real strengths of the Batman mythology is its ability to be portrayed in different manners, with different interpretations. This allows it to transform and evolve with the times and the audience, so that it remains both relevant and loved by the entirety of its contemporary, continuously changing audience.
Batman and many of his foes are more than half a century old. Most characters pass into obscurity after such a length of time - can you name most of the pulp heroes (and their enemies) from the 40s? I would doubt it. But because Batman, Joker, Catwoman, and other foes can be re-interpreted and re-characterized over and over again, they remain well-known and well-loved by modern-day audiences.
For instance - the Joker started as a creepy serial killer and robber. Then, for several decades, he was a (relatively) harmless clown and prankster. The 70s and 80s merged the two, into the laughing, but quite deadly, Joker that Nicholson's Joker was born from. In the decade or two since then, the Joker has evolved yet again - representing a deeper form of anarchy in some interpretations, and in others he represents a truer, more devilish form of evil, as the Devil Incarnate.
No interpretation is any more, or less, valid. They're all equally important, and each has merits that keep them interesting.
Yes, he was. He was a plump, middle-aged Joker.
So? There's nothing that requires the Joker to have a certain body type or age. It's the personality and characterization that counts, and it matches the Joker of his era perfectly.
On top of that, he essentially just played himself with make-up on and laughed a lot.
He was well-suited to the role (which I believe was written specifically for him), and that is not unheard of. But he was not playing himself.
Jack Nicholson isn't a super-narcissistic, homicidal maniac. He's an incredibly talented artist, who has deep respect for art in all its forms (he's said that the Art Museum vandalization was the hardest scene for him to do, personally). I think you would find that Jack Nicholson is quite unlike the Joker if you actually knew him.
And in many incarnations, the Joker does laugh quite a lot - at least once a page!
Bruce Wayne was actually his biggest flaw in his performance, ... He did not deliver well in that area at all. He did not give us the image of a billionaire playboy and a suave man. He gave us the image of a weirdo
He performed perfectly, and delivered the role as it was written. It wasn't written as a suave billionaire playboy - it was written as reclusive, eccentric, socially isolated man who has still not gotten over the death of his parents as a kid.
That's what cool about Keaton's version of Bruce Wayne. It shows just how damaged Wayne/Batman really is. He's not a normal person, even when he's not wearing the Batsuit. How could he be? How could a normal, suave person be the same guy who wants to put on a Batsuit and fight criminals at night?
You might not like that interpretation personally, but it's no less valid. Consider - there is NO definitive characterization of Bruce Wayne.
In many of the monumental comics (like "Year One") and the Nolan films, Wayne portrays himself as an irresponsible, selfish, care-free playboy - wandering the town in his fancy cars, dating a different supermodel each week, and partying hard. That's how the people of Gotham see him.
But in other media, like "The Animated Series," Wayne is a well-respected member of society. By the rest of the world, he's seen as an incredibly capable and intelligent businessman, and a strong, charitable humanitarian. There really isn't the "playboy" aspect at all (except for the hint that he can't commit romantically, but even that isn't consistent). Yet, this interpretation is seen as no less valid than the above, party-all-night version of Wayne. In fact, many swear that "The Animated Series" is the most "faithful" version of the Batman mythology entirely!
While the film was not tremendously groundbreaking like VintijDroidGutzz said,
To be blunt, you're simply ignorant on this point, because you're quite wrong.
"Batman," the 1989 film, was a game-changer in Hollywood and how America experiences movies. It also had a strong impact on the kinds of movies that are made and how they are created and imagined.
Do you know how hugely-anticipated movies are marketed and "hyped" today? The modern-day method and practice of "hyping" movies originated with the marketing of Batman.
at the guy arguing for it. i can see wanting one i guess but to group in and downplay the original Burton Batman movie? 
