I often think of this myself. On one hand, you've got the world's greatest tourist destination and the ultimate Vacation Kingdom, which is what Roy wanted to have in tribute to his brother. You've got innovative attractions, long-time classics, and general awesomeness.
On the other hand, it completely misses a lot of what Walt wanted. Sure, we all know he didn't want a clone of Disneyland in the MK (but eventually gave in to it), but I can't help but think that he would be drastically disappointed with the fact that his version of EPCOT never came to fruition. A lot of his creative, futuristic vision is all lost. No more future city, electric vehicles, circular-city-designed.
So all in all, I think he'd be proud of what is there, but he might be disappointed that HIS vision never happened.