As Order of the phoenix will be the first book in this game, I think that a level in the room of requirement will be a great way to introduce offensive spells, like stupefy andreducto, etc.
Also I think that a new way of duelling should be introduced, like when dumbledore and voldemort and harry and voldemort duel their wands connect, it would be great to be able to dothis in the game with friends, whoever pushes the fastest will win, this was only explored basically in years 1-4 in the last level.
I think that you should be able to go back into a classroom and re-do the lesson, this was not available in the last game and could be annoying if you are trying to teach someone who is new to the game all the spells/abilities, in the end I built my very own Hogwarts in creator so me and my friends could use that instead.
I do really like years 1-4 but I hope that years 5-7 improves on points that let the first game down.