I can't speak for others, but I can give you my OWN assessment and theorize as to why others may feel the same way...
One thing I can say for DCA is that it is a truly pretty park. On my first few visits there, I had much more fun just walking around taking pictures than I did visiting the attractions themselves. I also think that placing a Disney hotel adjacent to the park and with it's own entrance was a very innovative move.
I think the disappointment many people feel about DCA (myself included) pertains to expectations. For example, the signature attraction of the park is Soarin'. It is the type of attraction that you'd probably be impressed with if it was one of those motion simulator attractions at a mall somewhere. But as a Disney attraction, I frankly just don't get it. People rant and rave about it as the best attraction in the park and I personally think that says a lot about the park. If this attraction were in any other Disney park, I think people would be reacting differently to it. When they build it at Epcot, they'd better make improvements or I don't think it will be as well received (just my opinion).
The other big attraction is California Screamin'. There's a dilemma with putting this type of ride in a Disney park. First, it kind of breaks some of the traditional "rules" of Disney attractions, in that it has no themeing and is basically just another roller coaster. Sure, it is a steel coaster designed to look like a wooden one, but contrary to what you'll read, that's not the first time this has been done (Cedar Point has a ride called Gemini which is the same concept). Also, many Disney purists object to this type of ride because it is contrary to what Walt would have wanted in a Disney park. His whole point in getting into the theme park business was to create something different from what you could see at your basic amusement parks. DCA is the first and only Disney park to deviate from that philosophy. The other side of the dilemma about California Screamin' is that it is not exactly a huge hit with coaster buffs. As coasters go, it is a fairly benign and dull ride. Disney excels at THEMEING their rides and attractions. They should stick to what they're good at and what they do better than anyone else, instead of trying to compete in a market segment that is so clearly dominated by Six Flags and others.
Another problem with DCA is that a lot of the attractions are just off-the-shelf amusement rides. As stated before, what sets Disney apart from other parks is that you can see and experience things you can get elsewhere. People who support DCA will make every excuse in the book to justify the existence of these off-the-shelf attractions, but the park's attendance record really says it all...clearly putting these attractions in was not a wise move because they haven't exactly brought the crowds into the park.
Yet another problem is the lack of attractions that aren't simply copycats from WDW. And with the exception of Tower of Terror, which hasn't opened yet, the copycats they chose to make aren't exactly major ones.
The combination of amusement rides and WDW knock-offs leads to another problem I think a lot of people have with DCA...resentment toward Disney management for thinking we're all idiots. By building a park without a whole lot of originality and then filling it mostly with shops, restaurants and a handful of duplicate attractions, the Disney Company seemed to be saying, "We know we can totally skimp on this park because you'll still pay to get in since it has the Disney name on it. We'll just sit back and watch the profits roll in! Muhahahahahahaaaaaa!!"
Lastly, I think a lot of people have a problem with the theme itself. Before the park even opened, scores of newspaper and magazine articles speculated that no one would pay to get into a park about California when they were immersed in the real thing. But Disney seems to have essentially abandoned that theme anyway. Most of the attractions in the park have little or nothing to do with California (i.e. What the heck does "Who Wants to Be a Millionaire" have to do with California?? Isn't the game show itself filmed in New York??? What about A Bug's Land?? Are they trying to say bugs are somehow unique to, or representative of, California??). Consequently, the park seems to have no clear direction. Frankly that makes the park no different than a Six Flags or other non-Disney park. Disney parks have always been about having a clear theme, and then doing some incredibly creative things with that theme. DCA just seems to be sporadically put together.
Those are my personal thoughts. Does that help?
