Batman TAS is the type of show that even as a child I could recognize its quality but I never particularly enjoyed watching it then and now I'd still rather watch Brace & Bold, Beyond, Justice League Classic/Unlimited, Young Justice, etc. I don't want to use the word overrated because the series produced some LEGIT great episodes but I don't think I hold B:TAS in as high esteem at many others :/
I was the same way to be honest. I liked Batman whenever I caught an episode, but I wasn't mad when I missed it like I was with, say, Spider-Man or Tiny Toons. Going back to it, though, it was definitely great and a contender for the best written Batman ever.
Wasn't she a character that was created/first seen in the show and got so popular they made her an actual Batman comic character? I think it's because the show knew what tone and audience it was going for, while some of the comics like to make things edgy and it just gets out of hand
Edgy isn't really a problem with Harley. It's more the comics just don't know how to keep her interesting. They can't keep her around the Joker time because that limits what they can do with him (plus, their abusive relationship gets a little depressing), but her main gimmick is being desperately in love with him. So there's not much you can do there.
That said, she does have one of the highest selling books out right now, so what do I know.