It's just.... we now know that before the Joker was a psychotic, monologuing killer with aspirations of mass slaughter... he was a psychotic, monologuing killer with aspirations of mass slaughter. Wisely, he never gave the Joker a name or a backstory beyond what happens in the story, and he even directly invokes a "multiple choice" scenario concerning who he really was... but we still simply know too much about him. Some might disagree, but I think what makes the Joker work is that we don't know anything about him. We don't know why he is the way he is, he simply is. There was mystery to him. Now, even before he was the Joker he was a super-criminal. Instead of asking what made the Joker the way he is, we could be asking what made Red Hood 1 the way he is, because it's essentially the same question, and I think that cheapens the character. Additionally, it takes the character who at the start of the story we all pointed to and said "hey, is that the Joker?" and answers "yeah, there's no mystery here"
As for the Batman stuff, it's all really good. For some reason I like the haircut, even though I'm not entirely sure of the reasoning behind it. If it's just cosmetic, I'm fine with it. The pro to-Batman costume feels appropriately proto while maintaining that Batman has access to some high tech stuff. Batman is just smart enough to be able to put a brilliant plan together, but still green enough to get beaten up while pulling it off. I like the references to Batman 89, even though I kind of hate the movie. I like ACE chemicals being integral to the origin story, and I like Gordon appearing even though I wish he was in it more.
All in all, nothing is ever gonna replace Year One as the definitive origin story for me, but goddamn, this story mightily wins second place.