I'm just watching Joker is Wild / Badman is Riled for the first time after probably 2 decades of not seeing a single rerun of it, and I have to admit, my memory of Romero as the Joker was all wrong.
Within that silly, ridiculously modern world (which is an exact mirror of what the DC characters were doing in the comics back then, and was revolutionary and very grounded compared with the 50s stuff), Romero's Joker is quite scary. At least in his first appearance. The scene in which Batman takes his Pagliacci mask (remarkably similar to the one Ledger wears at the beginning of The Dark Knight) is quite creepy. Even though it's no surprise seeing his face, that hysterical laugh and the close up totally does the trick. Kinda the same with the news scene. He even looks creepy just playing baseball.
That episode echoes a lot of stuff we have seen in The Laughing Fish, The Dark Knight and the 1989 movie. If anything, I'd have reduced a lot of face time, so that the Pagliacci scene is his fist one and the audience really soils his pants.
I used to consider that the series only really had the best Penguin and Riddler (it really does, and they really fit that universe), and while Hamill, Ledger and Nicholson are way too good, Romero certainly did an awesome job.