Like it or not, Lego has once again managed an incredible game on the DS. Not without a few minor blemishes, though.
I write this after having played and beat Years 1-4 (and am currently at around 90% trying to unlock everything), thus my review.
The difficulty of this game overall is not too hard. There are a few puzzles that may take you a few minutes to figure out what they are hinting towards but everything flows very nicely. You walk through the movies quite accurately. Before you go through a level, you attend a class which teaches you a new spell. Unlike the movies, the order of the spells seems a little backwards here.
****SPOILER****
One of your most important/needed spells to open doors is actually one of the last you receive.
****END SPOILER****
On the DS version of Harry Potter, each spell has a unique symbol you must draw. An item will show up green, you tap it, and then swipe the symbol. If the item is purple, the Lego guys were kind enough to show you a picture of who in your party can complete the item. The item will be red, and a giant X on the portrait, if you do not have any characters in your party that can unlock it.
As you progress from year to year, your spell selection increases and unlocks things in previous play through's that were unavailable prior due to wrong character, wrong spell, etc. Throughout the games, you're basically hand-held by the game pointing you in the right direction. If you fail to read what they tell you, you could end up diverting in the wrong area. This is helped NICELY by the map system on the top screen which gives you useful indicators such has the unlockables left in the particular area, where you next contact is, and where you're supposed to head next. Overall I did not have any issues or need any walkthroughs for the game, but some younger audiences may or may not need them.
As far as controls go, you MUST use the stylus. ABXY do not have function in this game. You can move your characters either by pressing on the screen or by using the D-Pad. I found that after trying both just the stylus worked the best for me. Your right bumper is used to change characters. You can also do this by tapping your character (just wait until you need to tap yourself to cast a spell on yourself and you change characters). There are a couple of "tools" through out the game that have buttons around the edges of the screen to play. Your owl, your cape, the mark of Slitherin etc.
The music is classic on this, they play a little bit of everything from the soundtracks. After a while you'll find that you do turn down the volume a bit. Not that it's bad, it just is one of those things that begins to grate on you while you're trying to figure out what you want to do.
There were a few bugs in the game. I had a single freeze the entire time I had been playing. Luckily Potter's levels are only about 15-20 minutes in length and saves in between levels so I found I only needed to replay about 5 minutes or so. I also encountered a level where I cast a spell to lower a ladder behind me and then had an NPC block me in so I couldn't move. MOST NPC's in the game would allow you to push them out of the way. This one did not. I spent roughly 10 minutes trying to wiggle through a crack to get freedom. Had I not had most the unlockables I may have just restarted.
That is another complaint, you need to actually COMPLETE a level in order to obtain the unlockables. If you go back to play through a level and missed something in the very first room, you cannot just quit out. It does not save the unlocked item. You must complete that level for it to register. In the "main room" you will find information (like other Lego games) about which levels have items left to be unlocked, etc. Very nicely organized so you know which levels to delve back into.
Overall, this game has been like crack for me the past couple of days. I've played through it and now I'm working on going back and 100% completing it. I estimate my play time on it to be roughly 16-20 hours or so to beat the game. The saved game DOES keep track how long you've been playing but if you've set your DS down to complete other items with it open, it continues to count so I can't give you a more accurate play time. And just one play through will NOT nab you all of the characters , unlockables, etc so you will have to play through AT LEAST twice to get the full experience.