All the non-MK parks have problems that need to be addressed.
Epcot is the most problematic. As many have pointed out, its optimistic spirit has crumbled a bit since its EPCOT Center origins, and at this point, any real thematic cohesiveness in Future World is on life support. Many attractions are inferior to those that preceded them. The problem is that the park nonetheless easily provides a full day of things to do, many of which likely do pretty well on guest satisfaction surveys. In other words, I'm not sure its problems are really on Disney's radar of things to address in the long run, since it at least functions as a full day theme park.
DHS's problems are completely different. The quality of its existing attractions is very strong - the problem is that there isn't enough of them, earning it the reputation by many as a half-day theme park. It also has a serious deficiency of family rides, leading to extreme pressure on one of the few it has, Toy Story Midway Mania. The easy solution, of course, would be to add some high-quality and high-capacity family rides in the vein of TSMM, which would both fill out a day there and spread out the family crowds more evenly. A Muppet Studios expansion, some Indiana Jones or Star Wars attractions for the Lucas area there, some more Pixar attractions, or even a high quality Great Movie Ride renovation to make it more interesting to kids, would all be effective for this. Why Disney hasn't done this yet is beyond me. The one problem is that the park has a hodgepodge layout and unconventional thematic framework that would make expansion a bit difficult.
AK has problems similar to DHS's in that it lacks a full day of things to do for many people, but is fortunate in that its theme is much more established, making for a clearer direction of how to expand. It also has a much more organized layout, as well as clearer and more accessible plots for expansion. And with Avatar on the horizon, hopefully its half-day problems are on their way to being solved.
