Just churned through all 15 books in the last two months. I love the storylines and characters. There are a few little annoying things that happen, and a couple of minor plot flaws (in my opinion), but none of them bad enough to influence my enjoyment.

However, I have a real challenge with the lack of advancement in Harrys magic abilities. He gets some horsepower and a few new tricks given to him, but over the 10 years of the books, he really doesn't seem to improve beyond a brute force magician, even though he is exposed to all sorts of examples that are skill based not strength based. We know he has the ability to dedicate immense time to specific things. Staff, Chicago model etc.. We see many references to his recognition of the finesse that he does not have. I.e. Seeing the archive hold off a handful of Denarians.
Almost every magical conflict he gets into, he depletes his reserves with a few massive assaults, then needs to rely on luck or other people/factors to save him.
All of this just seems incongruent to me.
Apart from that, I loved the books, even managed to watch the TV series as well. Looking forward to more!