It's a very, very well done film and as a comic book super hero fan I think it does capture a certain flavor of comics from the period it takes place in despite it not being a "super hero" story.
But I already find myself putting it in the category of say, a Platoon or a Killing Fields. I cannot deny the overall quality of the film, at the same time I am not sure I will feel a need to revisit it all that often in the future. Whatever one might say of for example Logan, I know I will watch that again, and have. That's not putting Joker down, but some great films often have that "I'm not sure I feel the need to ever see this again" quality.
I will say I was totally engrossed and engaged. Never bored and were this decades ago and I came across this having never seen it before on cable I probably would watch it straight through to the end, which is a compliment.
Not sure how this affects WB's DC films going forward since I really am not sure how you can recreate this with some other characters they have really.