I think everyone here agrees that IP is secondary to execution when it comes to theme park attractions. The Harry Potter expansions represent a perfect marriage of a popular intellectual property with bar-raising delivery. Fast & Furious shows what can happen when a successful movie franchise gets slapped on a terrible ride. No IP in the world could have saved that attraction. If anything, the use of something like Fast & Furious on a slow-moving attraction just added insult to injury. Avatar is hardly beloved by movie-goers these days, but Disney fans are foaming over Pandora. Most kids today have never heard of Song of the South, but Splash Mountain is a classic. I could go on and on. IP can enhance, but it can't fix a poorly designed attraction or land.
Where we differ is on the popularity of specific intellectual properties. That's largely subjective, so disagreements are to be expected.
@MisterPenguin says that the Universal Monsters are a weak IP, but he's basing that almost entirely on movie grosses. It's true, most of Universal's attempts to capitalize on their classic monsters have been unsuccessful. At least when it comes to new movies. But that's very far from the whole picture. The reason Universal keeps trying to launch franchises like the failed Dark Universe is because they know there is a built-in audience for these characters. They can see it in the perennial sale of merchandise. Monsters may not be selling movie tickets like superheroes these days, but they are still big money.
A while ago, there was a listing of the 30 highest-grossing media franchises in the world. It made a lot of waves when it proclaimed Pokemon the king of all media. The runner-up was Hello Kitty followed by Winnie the Pooh. By that metric, Universal should be building a Hello Kitty land instead of just a small shop with a meet and greet. But I think we all know, the numbers don't tell the whole story. While Pooh and company are popular characters, they are not the primary draw at Walt Disney parks. Harry Potter, by the way, ranked 10th below something called Shōnen Jump. Yeah, never heard of it.
There are other considerations. For example, suitability. Fast & Furious was a perfect fit for a theme park attraction. It begged for something like Test Track. That would have been a slam dunk. I think you're more limited with what you can do with something like Hello Kitty, although a good creative team could probably design a kick butt Hello Kitty land. The monsters, to my mind, are very theme-park friendly.
Will the monsters appeal to everyone? Nothing does. But there are a lot of fans of these characters specifically and old school gothic horror in general who will find a monsters land appealing. The fact that Universal and Tom Cruise botched the Mummy relaunch won't factor into their decision one bit.
Of course execution will be key. It always is. Removing that from the equation, the classic monsters are as viable an IP as many others featured in popular theme park attractions.