As much as I admire Rowling's charming world building, she really does fall down on a theory of magic, seriously undercutting any chance the HP universe has to be compelling beyond mild entertainment.
Not sure I follow....... are you saying that the lack of a more intricate, self-consistent, logical system of magic greatly affected your ability to the enjoy the books or am I misunderstanding what your getting at?
Oh, I enjoy the books, but only as light entertainment. Many HP fans make much of the depth of the books, how they got darker as they progressed, character development, etc, but I find those to be weak arguments and the books to be a confection at most. Rowling introduces new magical rules as it suits the plot of the current book and so has numerous items which should but do not apply to the plots of earlier books. This doesn't particularly bother me because I never expected HP to be more than a beach read. But I can see where it had the potential to be a more compelling fictional universe and I think she sort of tries for that towards the end, but falls far short because there's too much she hadn't decided about the universe on the front end. This is a problem for a lot of serial entertainment, but it's a pretty basic rule that if you are going to invent a universe with extra physics (as would be required for magic) then it's a good idea to know how those physics work. She plainly doesn't know that and throws in magical laws as it suits - which does lead to a very confusing bit of business to explain how Harry defeats Voldemort.
A more serious criticism I might have of that ending would be that Harry really does not have a character arc throughout the series. He does not learn himself and magic and grow to be as powerful as Voldemort. He doesn't learn and grow enough to outsmart a Voldemort still far more powerful than he is himself. Still as much a little boy as he was in the first book, he stands up to Voldemort, just as he did at the end of Sorcerer's Stone, and more or less accidentally defeats Voldemort by having the author work the rules of the universe out around him so that he can. That's what I mean by saying the books miss really creating a compelling story and universe. The universe and the plots work out far too much via authorial deus ex machina instead of logical self-consistency. So, I can enjoy them for their charm, but I don't consider them worth much beyond that.