^I strongly disagree. Hamill's Joker was a fantastic performance in its own right and would be even if you had no idea that Hamill had played any previous famous character. He brought a lot of range and versatility to it, and was effective at conveying both the funny and scary sides of the Joker.
I agree when he shifted into that darker and more serious
tone of voice, it could be pretty effective. Unfortunately those moments were really few and far between on the show.
Most of the time it was just a lot of non-stop cackling and bad jokes-- which was about as annoying and unthreatening then as when George Romero did it in the 60s.