How much is this game like the first three?
And how different from the fourth one is it?
shareLate reply is late :P I'll do it anyways though.
Well, Order of the Phoenix has free roaming back (YESSS!) and that is one of the reasons why people loved the three first games, but this time around, Hogwarts look more like the castle that we see in the movies. There is a lots to do and just walking around the school makes you feel like you're there. The missions are decent, but seems a bit forced and rushed at times.
Harry Potter and the Half Blood Prince game also has free roaming, and the castle is way bigger in that game than it is in Order of the Phoenix. If you only want a Harry Potter game so that you can roam Hogwarts, I suggest getting Half Blood Prince.
Oh, and Deathly Hallows Part 1 & 2 does not have free roaming, as the goblet of fire, and I suggest you staying far away from those games. They're terrible.
Fear not the darkness, but welcome its embrace.