I'm about 18h in. I'd give it a 9/10 so far. I have a couple gripes, but the good far outweighs the bad.
Sometimes I've encountered things where I'm not sure if I'm just doing something wrong, or aren't supposed to be at that point yet. And it can be a little frustrating because after 15 minutes of trying different things I realize I probably don't have the spell I need to yet (although I'm pretty much past the stage of not having enough resources). The map is also huge...maybe a little too big. The open land south of Hogwarts has a lot of filler - a lot of villages with no character, and a lot of boring NPC's and Ubisoft-style side quests. The gear system is also kinda annoying... I'm giving my Slytherin the Dark Arts pre-order look, and every time I want to swap to a better piece of gear, you have to change the visual to the Dark Arts one. And it seems like you get a better piece of gear every 20 minutes, and run out of gear space a lot (I understand there are challenges to unlock more gear equipment space).
With that being said, it's been a fantastic experience. Hogwarts feels as magical and mysterious as it did in the books and in the movie. There are soooo many fine details and despite probably spending 10+ hours running around the castle, I can still find new places I haven't been to yet. I think they nailed the classes - come in, learn a spell or learn about potions or plants, and then go out and do it in the real world to unlock the next stage. The game runs really smoothly (some frame rate dips when it's rendering the next part of the open world). Hodsmeade is pretty cool...they basically combined it with Diagon Alley. I'm really enjoying the storyline and layers going on, from the stuff with your classmate to Professor Fig, to the goblin rebellion. Wondering if they'll be a cool easter egg near the end or at some point!