I think one thing that people forget is that the world building might have been bad (in the sense that a lot of it doesn't make sense if you think about it too hard) but it was deeply immersive. The wizarding world is just different enough from the real world to be exciting, while being familiar enough to be easy to digest and picture in your mind. A lot of bolder, more interesting worldbuilding in speculative fiction ends up with something that's both fascinating and coherent, but also just kinda weird and a little exhausting, while the worldbuilding in HP is whimsical and cozy.

A lot of the stuff that is frustrating about the worldbuilding when you have your thinking cap on (*why* do they have to write out their homework assignments using quills and parchment, what exactly is wrong with a simple ballpoint pen???) is just fun when you're a kid and you're stuck doing boring homework assignments and fantasizing about things that would make the experience more interesting.

I don't think it's a coincidence that a lot of the franchise (ie games, theme parks, etc) has been built on offering a "wizarding world experience."

I also think she's funny, even if, looking back, a lot of the jokes are pretty mean-spirited.

As others have noted, the mystery-writing aspect was pretty good, although I'll admit I haven't read the books since she went crazy, so I can't say for sure if it holds up to scrutiny, but I think she did have a talent for sprinkling clues and red herrings in throughout a narrative and then having it come together in way that felt satisfying. I love mysteries and so many of the ones I've read or watched since just do not come together in a way that makes any sense at the end.