The hallmark of the game, as with most of the Lego titles, is consequence-free exploration. As Hagrid, or Harry, or Hermione, or in fact any of 140 different playable characters (I saw Scabbers the rat and one of the Gringotts goblins also being played), players run around with abandon, and play and interact with all of the various environments, from Platform 9-and-three-quarters all the way up to Hogwarts and everywhere else in the first four Harry Potter books (that's from Harry Potter and the Sorceror's Stone up to Harry Potter and the Goblet of Fire, or "right, the one with the Olympics," as I called it). Gameplay consists of running and jumping and smashing and collecting and rebuilding lots of little Lego blocks. You can overturn tables and smash items, and then cast spells to rebuild them or just interact with other characters in a weird sort of wordless whimsical free-for-all.
The basic gameplay has you collecting Lego "studs," which can then be spent later for characters or items, but then there are also "gold bricks" hidden around that you can collect for -- well, I'm not quite sure. I tried to wrap my head about all of the little gameplay quirks, thinking that it would get me excited about playing another Banjo Kazooie-style collect-a-thon, but then I realized I was putting too much thought into it. While there is a lot going on in the game, the goal isn't to collect everything, it's just to collect whatever you want. And when you combine that with the fact that there's no real punishment to speak of (though there are enemies later on), Lego Harry Potter isn't so much a game as it is just a toy; a playground for kids to explore and press buttons in and see some flashy graphics.
Lego Harry Potter is not a bad toy -- there are a few puzzles, and one of the new additions in this version brings actual physics to some of the pieces that you find. One area had Harry actually building a staircase with Lego bricks, and the staircase could be built in multiple ways or up to new areas to earn extra goodies. There's also drop-in and drop-out co-op, and Harry and friends can combine their spells in interesting ways -- like spawning a puddle of water and moving it onto flowers, which then grow up into a ladder -- to open up secrets or move the story forward. If you (or, more likely, your kids) enjoy the Lego games, you'll like this one, too.
But in the end, I wasn't sold on the early version I saw -- it was too much chaos with too little payoff. There's no tutorial or guidance, so younger players have complete freedom to explore, but older players won't find any depth to speak of. And since there are no words in the cutscenes, you'll probably already have to know your dementors from your Hogsmeade if you want to really understand everything that's happening.
Then again, maybe that's not really the point. A fellow press member was watching the game demo with me, and when a Lego version of Hermoine's cat Crookshanks appeared on the screen, she yelled out, "Aww, kitty!" in youthful glee. If that's all it takes to get you excited about a gaming experience, then maybe Harry Potter in Lego form is right up your (Diagon) Alley.
Lego Harry Potter: Years 1-4 is due out sometime in June 2010 for all current-generation platforms.