I literally just made this switch. After being with Dish for about 10 years, I got DirecTV installed today. Been playing around with it for a couple of hours. The picture quality is definitely better. I'm watching football right now after watching a bunch yesterday, and the difference is significant. On Dish, there were always compression artifacts around the players when they moved, and I'm not seeing that at all on DirecTV. Couple that with the significant savings I got, plus Sunday Ticket, and I'm happy.
HOWEVER. The Genie lags far behind the Hopper 3 in many, many ways. First off, only 5 tuners (I have an HR-54) vs. 16 in the Hopper. No OTA support. No folders, which honestly amazes me. The hard drive is half the size of the Hopper's. The user interface seems less polished, and it's not quite as quick and responsive as the Hopper, either. None of these are deal-breakers for me, but you definitely want to go in with your eyes open if you make the switch.