I think you're confusing the space with the purpose. What we're talking about is execution and what they're trying to achieve. MMRR is trying to make you feel like a participant in a cartoon.
While the comparison to the original EPCOT attractions is valid, I'd argue the biggest difference is the EPCOT shows had more of a focused theme, and I just feel like GMR was more of a gussied-up diorama that didn't bring you into the subject emotionally. (Except for the Alien/Nostromo part, which kind of shows to me the immersive experience the ride could've been. That part is so good that I completely understand why they wanted to basically carve it out and put it in Tomorrowland as the original idea for Alien Encounters.)
The biggest general flaw with GMR is that if you had no relationship with the films originally, it's not going to move you - thus the frequent calls before it closed to update the ride. And that's a problem - if they had designed the ride to really bring you *into* scenes, the movie selection really wouldn't have mattered. Incidentally, these are the some of the same problems I have with the Na'vi River Journey too. A lot of the other dark rides work great because of sheer force of narrative and/or original execution and vision.
And no, it's not at all about narrow range of IPs - it's about finally having a deep, fun celebration of THE centerpiece of Disney history - and in a way that uses tech to simulate being INSIDE the animation as part of Mickey's world. I wouldn't have wanted a Mickey ride that just had Mickey for the sake of his presence. The lack of a Mickey-themed attraction didn't HURT the parks. But this, to me, feels like the right execution at the right time and it's a giant plus that it could happen.
Of course Disney shorts weren't as meta or completely nuts as what WB did. But the early ones of the late 20s and early 30s? Those are *absolutely* more wild than what came later when you got Mickey-as-hero with the cuddly, redesigned face, the Mickey and the Beanstalk era. Early Mickey was a somewhat mischievous rapscallion who got into crazy, illogical hijinx. The situation is where the anarchy lay, not the characters, generally, and that's the spirit of the new shorts and this ride. I mean, when I hear about this ride, I totally think of shorts like Plane Crazy and such. It's a very specific kind of energy and I *love* that.
(We could have a whole discussion about how early Mickey was someone who jumped into adventures and was jumped right in when reality broke, how 40s-50s-era Mickey seemed kind of terrified when situations spiraled out of control, and how Sorcerer's Apprentice is where those two concepts fused, but I think that's a discussion for a different time.
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