Why I Loved Nolan and Heath's Joker

I think this excerpt from Greg Burgas' article about the legendary Engelhart/Rogers/Austin Detective Comics run explains it best,
as it describes not only that particular Joker to a tee, but The Joker from The Dark Knight as well:

Englehart's final story is a two-part Joker tale about the laughing fish. It is a story with ties to the past, but also, like the other stories of the run, modern and forward-looking. The Joker is portrayed here far better than he usually is—most of us, I would guess, are tired of the Joker as completely insane mass murderer. In these stories he kills people, naturally, but he has a "purpose," as twisted as it might be. The Joker's insanity is always more interesting when it has a clarity that he thinks of as sane, and his scheme here—to poison fish so that they have a "Joker grin" on them, and then trademark the fish and make a fortune—is gleefully twisted and magnificently insane.

In the two issues, he "only" kills three people, so it's not like it's totally indiscriminate. What bothers us about the Joker these days is the randomness of it all, and that also lessens his impact. Here, because he has a purpose, it's a bit more chilling, as he's portrayed as a criminal mastermind who kills to get what he wants. The argument could be made that the out-of-control Joker who kills masses of people is more scary because you never know who he's going to kill, but that Joker, Miller's and Moore's Joker from the mid-1980s through to today, has become so far removed from reality that he's not terribly interesting anymore, and therefore far less frightening. Englehart's Joker is creepy specifically because he has a plan. This Joker is much like the original Joker, who stole jewels and killed the owners for the sport of it. Englehart hearkens back to that first Joker story (from Batman #1) with the famous challenge on the radio to the police, which, in 1977, now becomes a televised challenge. He kills his two victims ingeniously, and outwits Batman until our hero gets help from an unexpected source—the ghost of Hugo Strange. The third victim of the Joker in the story is one of his own henchmen, whom he pushes in front of a truck when the thug questions the plan. It's this portrayal of the Joker, the one seemingly in control of his mind but likely to suddenly snap, that makes him scary—not the Frank Miller version who casually slaughters an entire studio audience, or the Moore version who shoots Barbara Gordon for the sheer hell of it.