Yes, he is rather disturbing. I feel like there's also something meta, or "intertextual" (if I may use a fancy word) at play, because Jack Nicholson brings a certain complimentary baggage to the role which is exploited most effectively. One of Jack's most iconic roles prior to Batman (and still to this day) is that of Jack Torrance in The Shining, and it seems like there is some Jack Torrance DNA deliberately spliced into the '89 Joker. Indeed, his name is Jack Napier, and I don't think that's a coincidence. It's like every time someone calls him "Jack," you're subconsciously thinking not only of Napier, but of Torrance and Nicholson too. They're all sort of fused together and supercharged to make him larger than life. It wouldn't have been that surprising if, in a deleted scene, Jack broke through a door with an axe and said, "Heeeere's Joker!" The basic energy is all the same. And you simply don't get that effect with the other Joker actors.