I'd bet they look every bit as good as the OTA signals will. Even OTA is compressed. DirecTV uses MPEG-4 instead of MPEG-2, so the reduced bitrate shouldn't really affect the quality of the picture.
Unless you have golden eyes, a huge screen, and high end everything else, I don't think you'll notice a difference at all.
I can tell the difference between OTA HD and MPEG4 HD over satellite, plus as soon as it even sprinkles HD reception gets crappy, where as OTA never ever goes out (unless their transmitter dies).
Still I am excited to have locals on sat, that just means one less diplexer in my wiring rats nest.
BTW, for those that did not know, you can still diplex OTA on the HR20/21. You just have to work a little harder, I did that while the installer was there, he kept telling me that would not work, and then boom, I got KCCI-DT in perfect, he was shocked.