The second in the Lego harry potter series of game, encompasing the final films.
One of the major things that differs from the first game is the graphics. Both the lego and normal 3D environments have a much higher resolutiion and quality, in addition to the "magic" effect graphics. This coupled with some new gameplay challenges, like duelling, add lots more variety to this game.
Again, there is no voicing in this game, but it does expand the soundtrack to include music from the later films.
Another change worthy of note is that this game does not crash intermittently like the first lego hp game. It does however suffer from end-of-level saves only, which means that if the game bugs out somewhere [which it occasionally does] you'll have to restart the entire level.
If you played and liked the original HP lego game, then you'll definitely enjoy this one.