Dont know quite what it is, remember seeing Order of phoenix at the cinema, and thinking okaish, but then when it came on Sky Movies, and watched four times, really grew on me, likewise with Half blood prince, Azkaban.
JK Rowling has moulded the stories really well IMO, the selfless Harry the teenage pangs, the relationships with the adults, Harrys parents lurking inthe background, dobby, Gringotts, Hagrid, smashing cast and ensemble.
Thank you JK Rowling