I adore the Lego Star Wars games. Some of the other Lego games have been hit or miss, so I was curious when the Harry Potter one came out how it would be. It's really quite fun! I find some parts of it annoying, but in general the humor is quite funny and they did an awesome job of capturing some of the key moments in lego fashion. Here is my walkthrough for Lego Harry Potter, being written down as we go! Note that of course your brick count and stud count may vary based on how you choose to do things - I provide mine just to give you a general idea of how we did.

Post in the forums if you need help!

Getting Started
Basics
Extras to Buy
Characters

Year 1
Getting To the Alley
Getting To Hogwarts
Learning Levitation
An Ogre has Layers
Learning Lumos
Snape's Class
Herbology Class
Playing Qidditch
Cloak of Invisibility
Hagrid in the Forest
The Final Battle

Year 2
Landing in an Evil Shop
Getting to School
Blue Imps and Hagrid's Area
The Quidditch Match
Learning Expelliarmus
Getting Into Slytherin
Moaning Myrtle
Playing with Spiders
Taking Down the Snake

Bonus Levels
Bonus Level 1
Bonus Level 2 / Builder 1 of 4
Bonus Level 3

FAQs
Sparkly Red Items
Saving Games

Items to Earn / Buy
Red Bricks
Characters to Unlock