Casting spells is a lot of fun: Each spell has its own characteristic button combination, which you must copy exactly as it comes up on the onscreen prompt. Reducto is mapped to the square button because it is your main attack; however, other spells like wingardium leviosa require you to press the triangle button three times in quick succession. Harder spells, like transfiguration, require a mix--for example, you press the square button twice and then the circle once. This is an interesting way to cast spells--rather than just having them mapped to the existing buttons--and keeps you on your toes throughout the game. The gameplay doesn't actually freeze while you cast spells, which means that you still come under attack during combat. This is actually more enjoyable because of the challenge it sets: It simply means you have to prep yourself to get the button presses right the first time around.
There's no sweeter sound than crashing Lego blocks spewing forth mountains of treasure.
While combat still plays an important part in Lego Harry Potter, the emphasis on exploration and collection means you are encouraged to smash as much of your Lego surroundings as you can in that extremely rewarding gleeful-sense-of-destruction kind of way. Doing this reveals an overwhelming amount treasure, from studs and secret chests to wizard hats and red bricks (which unlock special spells in Free Play mode). Of course, this wouldn't be a Lego game without some light platforming and puzzle-solving. Outside the environmental puzzles you are required to solve to progress through the game, you only encounter two other types of puzzles: a quick-and-easy Lego jigsaw puzzle and one where you are required to match up three pairs of objects in the order you see them. As for the platforming, the game prompts you whenever you need to jump by revealing four small blue arrows on each platform that you need to reach. While neither element is particularly challenging, they're fun all the same, and given that there's so much to do all the time, this aspect is not bothersome.
What is bothersome is the game's uneven combat difficulty. By far, the toughest battle in the game takes place between Harry and Draco Malfoy during the middle of Year 2, where Harry must defeat Draco in a series of short fights that test the repertoire of spells you've learned up to that point. By contrast, one of the easiest battles in the game is the final one, where Harry must defeat Lord Voldemort (or Voldy, if you will) at the end of Year 4. The fact that this battle is so unchallenging and over so quickly is disappointing and deeply unrewarding. This is not the only instance of this: More often than not, Harry faces his toughest fights at the most random moments, with no real explanation as to why, which makes things feel slightly disjointed from time to time. The game can also be a little behind the action: Sometimes it can take up to five or six seconds for the game to catch up and update the map with your next task after an objective has been completed. There are also some instances of slow loading times, but this doesn't happen often and isn't enough to take you out of the experience when it does occur.
Lego Harry Potter: Years 1-4 for the PSP is an exciting adventure with loads of variety and replay value. There are rich environments to be explored, countless studs to be collected, and a wide array of spells to learn and practice. If you're willing to forgive the minor glitches and focus on the carefully constructed narrative and diverse gameplay with all its characteristic Lego idiosyncrasies, you'll have a wizard of a time.