TLDR it's a fairly cheap, casual, Quidditch game where you create a fully customisable team and go from The Burrow to the World Cup. If you don't find that appealing, don't buy it.
Like I said, you start at the Burrow which is the Tutorial stage. It takes you through all 4 roles (Chaser, Beater, Keeper and Seeker) and gives you the chance to replay each tutorial as much as you like. You have to create each player on your team at this point, but you can edit their appearance later. Finish the Tutorial by winning the Weasley Cup and you progress to Hogwarts.
Much to some people's disappointment, you don't get to pick from every character ever mentioned in the books to fill out your team, you play using the team you generated in the tutorial. Win the House Cup, which just means winning the bracket system tournament at the end, which hilariously led to me winning my first try despite having lost all the warmup matches.
Win that and you go to the Tri-Wizard Cup, then the world cup. I have to say I feel terrible every time I nail a beuxbatons (the French school) Chaser with a bludger and see little Gabrielle Delacour's name pop up.
The gameplay is simple yet entertaining. The thing I find most annoying is that sometimes the quaffle seems to be magnetically drawn to the keepers and sometimes you will be able to lob the quaffle at that same keeper's head and score.
If you're looking for an in depth quidditch simulator, firstly I understand entirely, that would be amazing. Secondly, this is not that. This is goofy, slightly arcadey game that is obviously designed with younger audiences in mind which given that it's based on a Children's series is fair enough.