Just moved over to Dish from DirecTV (long story) and so I was able to compare pretty quickly the diff. I would say there is a BIG difference between DirecTV and DISH HD. DirecTV, overall appears much better. But, it's not every channel but certain ones for sure.
For example, ESPN HD, the letters in all the pretty graphic boxes are ghosted sometimes, and not others. It's far more pronounced on my 46 Toshiba than on my 32" Samsung, but it's there nonetheless. So far, I'm very unimpressed with DISH HD.