It doesn't differ much from previous Lego games, but the gameplay here is incredibly enjoyable and addictive.
If you've ever played one of Traveller's Tales many Lego titles, you'll probably know what to expect from this one; there are a variety of levels to complete, each of which coincide with the plot of the series. As Harry or one of his many companions, you'll be able to jump about and cast spells to manipulate or smash items around you, which is essential when it comes to finding your way forward. Each level contains a few straightforward puzzles to solve, as well as Lego objects which you can build, and a good majority of these things are important as you'll need them to proceed through the level, though there are also a few puzzles and objects crammed into each level that serves the purpose of helping you gather collectable items or merely just there for the fun of it. These levels are enjoyable and memorable.
As well as the levels, Harry and friends can access a hub world, in the form of Hogwarts School. In between each level you'll find yourself dropped here, and it is here that you can learn new spells or potions to assist you in later levels. On top of that, there is a lot of scenery in Hogwarts that you can interact with; you can smash or levitate plenty of different items which will net you some more goodies in the form of studs, characters and bricks. Once you've discovered a collectable in either a level or the hub world, you can buy them in Diagon Alley using the Lego studs (currency) you've accumulated from just about everything you've smashed and influenced throughout the game. Collectables include unlockable characters, red bricks that will grant you new abilities (such as being able to collect ghost studs) and gold bricks which enable you to unlock bonus stages.
Smashing and manipulating everything is an addictive activity, to the extent that revisiting stages becomes desirable to ensure that everything is completed. You may notice pieces of scenery that can only be tampered with by characters with particular abilities, such as being able to open safes or use dark magic. Unlockable characters have access to these different abilities, which makes returning to levels via the Free Play mode a very worthwhile activity, since it'll net you further collectables.
The levels themselves are not at all difficult; the puzzles are simple and the few enemies that oppose you in the game can be defeated with relatively little effort. Not only that, but you have unlimited lives, and the game does not punish you too harshly for dying.
While the gameplay holds up very well and is incredibly enjoyable, that is not to say that there are not any flaws. Lego Harry Potter does not feel completely polished; there are a fair number of glitches that I've encountered, most of them being merely annoying but there were a couple of glitches that required me to start a level over. The targeting system for casting spells functions fine a fair portion of the time, but there have been a few issues where I could not shoot my spells at the target I wanted to. However, these issues are not altogether too common and do not take away too much from the fun experience.
Graphically, the game looks great; Hogwarts looks incredibly vibrant and is just as good to look at as it is to explore. The levels all look great too, each fitting the moods they try to convey. The music is essentially the same as it was in the films, and it is just as charming and nice to listen to as it was then, again fitting the mood nicely.
The gameplay may be more of the same in regards to the Lego games, but it never stops feeling enjoyable in this game. Collecting studs and collectables is incredibly addicting, and the levels stay true to the books/films while retaining a level of silliness that only the Lego brand could pull off in such a charming fashion. It's a simple yet satisfying game that will definitely appeal to those looking for something light-hearted and straightforward. I highly recommend picking this game up if you're a fan of the Lego games, or of Harry Potter.