Once you step inside, it feels like you're really there. Everything is so realistic and the people are always in character. It's amazing. If you only do one thing while at Universal, you should just walk through the WWoHP. The rides are great, too. And the Butterbeer. Try the frozen. You will thank me. The lines for pretty much everything may be long, but there are usually things to entertain you while you wait.
One big suggestion I have is to buy a wand. Yes, they're expensive. And yes, you can only use them while at the WWoHP. However, I think they are a great addition to any vacation. They help keep kids entertained and add a bit of whimsy to your trip. Some of the 'spells' are a little difficult and you may need to try them a couple times before getting them to work. Even as an adult, I had some difficulties. But my son absolutely loved it and I don't regret buying a wand one bit. To save some money, only buy one wand for the entire family and take turns.
If you really hate the idea of buying souvenirs early in the day, you can try buying them on your way out of the park at the main souvenir shops in the parks. They do have a great selection of Harry Potter stuff. However, they don't carry everything so if there's something that you really love, just know that the only place you may find it is in the shop that you originally saw it in.
The only ride I rode on in the WWoHP is the Flight of the Hippogriff (which is located in Hogsmeade). It was very fun! I loved seeing all the cool things like the actual Hippogriff and Hagrid's Hut. Plus, this was my son's first ever 'coaster'. It was the day before his 5th birthday so he was a little scared, but after the ride was over, he told us how much he loved it!
The biggest reason for me to pay for park hopper tickets is to ride the train. I mean, come on, ever since I watched that first Harry Potter movie, I have wanted to ride the Hogwarts Express. And believe me, it's worth it. This is not just a way to get from one park to another. This is a complete ride/experience in itself. You hear and see the shadows of Harry, Ron, and Hermoine outside your room. While you watch the 'window', there is a different view depending on which way you are traveling (from Hogsmeade to Diagon Alley or the reverse). The only downside of our two trips was that our son didn't get to sit by the window either time because people were very selfish and thought their families were more important that ours (even though he was clearly wearing his birthday button). So be advised. Unless your family is larger than 6 people, you will most likely be sitting with another family.
