I never really liked any of the HP games, so when i call this one the worst, i must really mean it!
Gameplay....Though this part of the Harry Potter games does have an interesting touch [the mouse is your wand] this gameplay add-on really wasn't that great. Occasionaly you'd be trying one spell, and because of a little twitch, you'll end up casting something else, or more often than not, nothing. Also, the library of spells, thus far at least, is very limited. Nothing else is added to this game in terms of gameplay. Same old, cast a spell at an obvious protrusion to win something you can't quite care about, only now, you've got to do it all across Hogwarts. Yes, you'd think that being able to explore the whole school would be 'awesome,' while in reality, it just adds to the pain of your tasks. For example, getting all the members of the DA into the Room of Requirements requires you to find them all. They're spread out between the four corners of Hogwarts, and can be found with the Marauder's Map [whose footsteps are extremely slow, and often covered up because of bad camera angles]. However, they assign you tasks which, often, result in you going to another corner of the school, to discover you have to go to another corner, and then finally go back to the first corner you were at. In such a big school, you'd expect the first lesson to involve a 'teleport' spell? Also, not all the doors are open to you, as advertised. Good luck seeing the girls' dormitories, [well, Hermione is allowed into the boys'] or seeing the Divination room etc. etc. These points mentioned in this paragraph are the biggest negatives in the game [there are more].
Graphics.... well, i'll be honest, i'm impressed with the environments, the bloom effect is well used, and the fx when casting spells is nice too! The characters do look quite a bit like the movie counterparts, but not really.
Sound... Bad voice-acting is my only beef with the sound in this game. Otherwise the ambient sounds and the magic sfx are pretty decent. Nothing much to complain about here!
Value.... don't buy. Even if you're a crazy fan of the series, its not even worth the rent!
If you do buy it, good luck not dying of boredom before getting all the DA members to get together!