The Lack of checks and balences at both the ministry of magic and at hogwarts that gave Deloris Umbridge so much power and the way everyone just let it happen despite the fact that sending everyone home was a quite viable alternative (Closing Hogwarts, a play that would have made the ministry of magic very unpopular) to letting her run the place. A bit like putting a vampire in charge of a blood bank !

As a character she was quite unnecessarily cruel which didn't really do anything for anyone.

Harry has obviously entered puberty, want an amazingly egocentric jerk ! Ok so he has a lot of **** to deal with however, maybe I am showing my age, if he were my ward he would have been treated very differently.

Dumbledor behaved like a schoolboy, very irritating ! To my mind this was only necessary as a device to elongate the already overly drawn out plot.

This was a big disappointment after books 3 and 4 witch were brilliant !