LEGO Harry Potter: Years 1-4 is set in the Harry Potter universe with the usual batch of characters including Harry Potter, Ron Weasley, Hermione Granger, Rubeus Hagrid, Albus Dumbledore and Severus Snape. This title follows the adventures and trials of the trio as they progress through their first four years at Hogwarts, with each year consisting of six levels. This comprises of the following tales:
LEGO Harry Potter contains game-play very similar to the previous LEGO titles, but is structured more like a traditional action-adventure game. As with previous LEGO games, different characters have different special abilities within the game, and puzzles often involve finding the right character to perform the right task to solve them. Characters in the game also have a selection of spells they can choose from, and puzzles often involve using the correct spell to solve them. Cauldrons can also be found around the game world with icons over them indicating certain potion ingredients that need to be found around the level and placed in the cauldron; once this is done the potion inside can be drunk to convey powers such as invisibility, transformation into another character, super strength, or rapid aging. The cauldron may also clear obstacles in the game by exploding.
Much like other LEGO games, LEGO Harry Potter has a large number of collectibles for players to amass; there are over 100 unlockable characters, 200 golden bricks for players to collect, and purchasable spells. Levels also include "students in peril" which players can rescue as well as Hogwarts crests that players can collect, both of which yield golden bricks.
One major change from previous games is the way LEGO Harry Potter treats the hub system. Like previous LEGO games such as LEGO Indiana Jones 2: The Adventure Continues, a hub world gives players a place to explore while also allowing them to go between levels. In LEGO Harry Potter, Diagon Alley and Hogwarts function as hub areas; however, Hogwarts is a constantly changing environment and includes a number of puzzles and opportunities to unlock new characters within itself. Nearly Headless Nick acts as a tour guide in Hogwarts, leading Harry and his friends to their next story level via a trail of "ghost studs." Diagon Alley contains shops which allow players to exchange their studs for unlockables such as new spells, extra characters, and special cheats. Much like its predecessors, LEGO Harry Potter also includes a number of bonus levels for players to play and includes the option for players to customize their own bonus level. The game can also be played split-screen with two players. Unlike other LEGO games, players can change characters while free roaming around Hogwarts with the use of Polyjuice Potion from a cauldron. This is brought into play because Hogwarts itself has collectibles that require the abilities of characters outside the main trio.
While at Hogwarts, Harry, Ron, and Hermione will learn a number of spells, as well as partner with other characters that know spells they haven't learned yet during levels. Several silly spells can be purchased at Diagon Alley, but they have little to no effect gameplay-wise outside of being entertaining, such as the spell that makes a plant grow out of the top of someone's head. Several useful ones are listed below:
The Nintendo DS version of the game features a simplified version of the game mechanics of the home console version but lacks the co-op support of the home console version. Hogwarts and Diagon Alley hubs are replaced with a single Gryffindor Common Room hub.
The game requires 6.3 GB to install on the Xbox 360's HDD.