I actually just had a similar experience with one of my friends. He's 23 and went to WDW for the first time and only spent one day there. They went to Epcot for the day and his reaction was that 'it's for 10-year olds'.

I used to be one of those folks that thought WDW was for little kids and wasn't all that exciting, too. Then I went twice and became a DVC owner

MK in particular I think has some issues winning over non-Disney folks. It's still not my favorite park by far, although I do enjoy it. There really is a lot there that's very "Itchy and Scratchy Land" in MK, and if you don't have an appreciation for it, it comes off as pretty lame. If you don't feel the magic, and you don't have an appreciation for everything that goes into the place, what is there for you at MK?

Let's be objective of a moment here. If you strip off the theme of these rides they're not extraordinary. They may have been state-of-the-art when they were made, but many of these rides now have some seriously outdated technology. Big Thunder and Space Mountain are awesome rides, but if you ignore the ambiance, they're pretty mediocre roller coasters. If you go to pretty much another other amusement park you'll go higher and faster - but you won't be riding through the dark in a space ship! If your expectation of a roller coaster is a 200ft drop at 80mph and inversions, Space Mountain just isn't all that impressive.

The 'dark rides' are in no way technologically advanced and tell stories that a lot of kids haven't really been introduced to in the same way that the rest of us have. If you didn't grow up watching Pooh on TV, is that ride all that much fun, or impressive in any way? If you don't have an appreciation for the Carousel of Progress (what it was when it was released, what the history of it means, etc) - it's it just an obsolete ride with an annoying song?

MK walks a tough tightrope as far as attractions go. It immerses you in a world of fantasy conceived almost 50 years ago. There's a need to stay true to the original vision and maintain the classics that the current fans love while making the park appeal to upcoming generations. It's a hard balance to maintain for sure.