Coming up with the worst-themed attractions in Walt Disney World was tough. This is because even the worst-themed attractions aren't that badly themed. And it's important to remember that not all of the worst-themed attractions are bad attractions in and of themselves (and should still be experienced at least once if possible). The same holds true for the best-themed attractions list - some of the best rides in Walt Disney World didn't make that list simply because the actual theme isn't top 10 material (i.e., Soarin') - but they're still terrific attractions.
So with that said, below are the Walt Disney World attractions that do the worst job of theming due to any number of reasons: having the least attention to detail, having shown their age to the point that it removes you from the fantasy of the experience, or simply lacking the "magic" of enveloping the guest in the experience.
Never mind that the subject of this attraction is woefully outdated and should be replaced immediately. That is beside the point. The real point here is the theme of this attraction is lacking horribly and has almost nothing to do with the 3D film. Honey replaced Captain EO in 1994 and at that time, there was still clear memory of the movie that inspired the idea of the attraction; it was still somewhat relevant. But it's clear that the minimum was done to give the theater a personality change after Captain EO. The pre-show room is bland and has basically no theming itself (compare/contrast that with Muppet Vision 3D), and the same basically holds true for the theater itself. This attraction relies almost completely on its 3D movie - which is a bad thing. At least if the theming were tremendous, the quality of movie itself might be forgiven (as with Star Tours).
Maelstrom, Epcot
This is a great example of what I consider to be a terrific attraction (one of my favorites in Epcot) whose theme (mostly due to its age) is starting to take away from the experience. This mostly has to do with a few of the older AA's having a slightly tougher time moving (the long, ferret-like Polar Bear, for example) and the oil platform scene after the little drop back, back down the falls. The lighting is such that you can easily see too much of the ceiling and walls - many of which the seams are very apparent and it takes you right out of the illusion of the scene. A little TLC would go a long way for this one. It deserves it.
Backlot Tour, Disney's Hollywood Studios
Now, the Backlot is not a typical attraction. It's not trying to fool your senses into believing you're in this fantastical setting. It is however, dependent on the content as the theme. And that content has dwindled for years. It's to the point that so much of what it had is gone, that there simply isn't that much to see any more. If the theme of the Backlot Tour is to show you a working backlot full of movie props and such, it's now way past its expiration date.
Turtle Talk With Crush, Epcot
Like Maelstom, this is a quality attraction that should not be missed. And while it doesn't have a bad theme, it just doesn't have a great one, worthy of the innovation of the main attraction (Crush's interactive Q&A with the audience - a technological marvel, especially at the time it came out). The pre-show area does have quizzes and different interactive and educational games for the kids to do while waiting for the show, but it just seems that this could be a much, much bigger deal of an attraction if they went all-out when designing the theme. More attention to detail - any attention to detail - in the Crush room would have sealed the deal.
Stitch's Great Escape, Magic Kingdom
I'm in the minority when it comes to opinions on the entertainment value of this attraction - I don't think it's all that bad. It has some very advanced audio-animatronics (Stitch) and even uses KUKA robots (the massive arm-like canons) to add a bit of a "wow" factor to the ride. Stitch took the place of Alien Encounter (which was a superior attraction), and as with Honey, I Shrunk The Audience, the minimum was done to give the attraction a personality of its own after having taken over a completely different attraction. The pre-show room that has the TVs hanging from the ceiling has a very similar feeling to the pre-show room at Honey - no theming at all, just TVs. Quite simply, lazy design. And while the next room has much more to offer, including another very good AA, the rest of the attraction does very little to sell the guest on the depth of the story - in other words, the theming is shallow and is one reason why many consider this attraction to be lacking the "Disney Magic".
Tomorrowland Speedway, Magic Kingdom
This attraction really has no place anywhere near Tomorrowland. And it takes up massive amounts of real estate that could be better used for something else futuristic that would make Tomorrowland truly phenomenal. Or, they could radically change the theme to make it an ultra-futuristic racing game so that its theme actually jives with its location within the park. Nothing about the attraction's theme makes sense as is.
Primeval Whirl, Animal Kingdom
I can see what Disney was trying to do here. The aim was to create an area of the park that simulated a road-side carnival. If that is the aim of the theme design, they hit the nail on the head - job well done. I just think it's a bad (and ugly) idea. Another example of a huge waste of a massive amount of space that could be utilized for something truly cool - another huge Dinosaur-related "thrill" ride or even an actual fossil museum with incredible interactive educational experiences. Worst of all, it appears as though Primeval Whirl is simply a cookie-cutter "wild mouse" roller coaster with an ugly coat of paint reflecting an ill-conceived idea for a theme. Dino-Rama is the one big blemish that resides in an otherwise incredibly themed theme park.