This is a Disney forum and there will always be people who say bad things about the competition without ever experiencing it, which is really a shame.
Whether or not you're a Potter fan or a Universal fan, there is simply no way an expansion like this can be written off as "nothing to worry about." What they were able to do here is something that completely blew me away. The level of immersion is like nothing I have experienced either at WDW or Disneyland. The closest thing I could compare it to, however, would be New Orleans Square at Disneyland.
Like New Orleans Square, my friends and I have spent hours walking around and taking in all of the atmosphere Wizarding World offers. There is so much to look at and piece together (Hermione's Time Turner is in one of the windows, daintily strewn about as if it has yet to be used) that I am always pointing out something new.
The shops are small, yes, but they are not meant to be warehouses. Part of the fun is squeezing past shelves to find more things around the corner. The shops in New Orleans Square are just as small, but the demand for Nightmare Before Christmas merchandise is not as high as the demand Golden Snitches, Sneakoscopes, Screaming YoYos, and Marauder's Maps, all of which you can only find in their respective stores within the Wizarding World. In fact, almost all of the merchandise here is custom made exclusive for the Wizarding World (including candy at Honeydukes) and all come in very nice, expertly designed packaging. In fact, finding a "Wizarding World" logo on anything is hard to do. You didn't buy that Fanged Flyer at The Wizarding World of Harry Potter, you bought it at Zonko's Joke Shop.
And then to round out the land are three great attractions. The other two have received modest makeovers to theme them properly (something that was done right, even though the Dragon's queue is much more bare) but the main attraction, Forbidden Journey is unparalleled as it stands right now.
The ride is breathtaking, but I was way more impressed with the technology behind it. They created a thrill ride with the same loading capacity of that of Haunted Mansion. The unique ride vehicle, coupled with animatronics, special effects, and the soundtrack just provide an amazing experience. The inner-castle queue is so well done. Something that has annoyed me as of late from Disney is their unwillingness to theme any attraction ceilings. They leave spotlights, AC ducts, and all the inner workings exposed. As for Hogwarts, the only things that could possibly clue you into the fact that you are not in a real castle would be the exit signs.
There have been some problems with guests not being able to fit, yes, but that happens everywhere. There are some guests who can not fit on Rock 'n' Roller Coaster and there are some who can not fit on Forbidden Journey, but that's just the way it is. They certainly are not turning away every other guest, but there are some who just can't safely fit into the restraint system of the ride, which is pretty intense in movement. Safety will always be a number one priority.
All that said, Universal has seen these problems and are working to fix them. All doors of the shops were recently changed to swing out into the street instead of into the shops, making it easier for people inside. Several shelves in Honeydukes were restructured to make traffic flow easier. Extra Butterbeer and (appropriately themed) drink carts were added since opening, and the strong rumor is that Universal Creative is working on a larger vehicle for Forbidden Journey.
It has been open for just about a month now. There are still things that need to be worked out and many things to be tweaked in the coming months. If you don't want to experience it, Disney will always be there, but if you are looking for a level of detail and immersion Disney has not been able to provide here in Orlando, a trip to the Wizarding World should be in your plans.