Well, since everyone has covered the 3D screens, I guess for me it just comes down to a feeling. When I leave Universal, the feeling is 'meh.' Ambivalent, not unimpressed, but not changed in anyway. Cool- I had fun, rode some rides, ate some mediocre theme park food, and (one time) stayed at what I felt was a "wannabe" Disney resort.
With Disney, I feel changed whenever I am there, and after I leave (here I am on a forum dedicated entirely to the establishment and it's been 2 years since I was last there). It just follows you. I don't know if I can articulate, but some kind of mix of inspired, excited, curious; essentially the definition of "joie de vivre." I'm not trying to sound overly dramatic but it just makes me more excited about life. Where else can you 'travel the world (showcase)' in one day? I could go on and on, the thematic elements that are just so perfectly executed, I am transported riding things like Tower of Terror, Kilimanjaro Safaris, Splash Mountain, - I'm preaching to the choir, but still. And the resorts - I can be in the 1920's at the BoardWalk, sitting on the beach in the Keys at Old Key West, in vintage Hawaiian/Polynesia at the Polynesian, or an equine enthusiast in elegant Saratoga Springs. And that's breaching the surface.
For me, Universal is what it is - a theme park. Disney is an escape. A chance for people to see the "world" who otherwise may never get to ACTUALLY see the world. I am almost 30, and have felt the same way about this place since I first started going when I was 8 or 9. My parents still make fun of me, when we had to leave on our first trip there I hoisted myself to the bed post and wouldn't let go. I still feel that way but I'm a little more mature about it now. I think. Ha.