For me the two ATSC tuners in the HR20 is a big plus for folks that don't have their local HD channels via DBS. Another plus for the HR20 is that the EPG has all the local ATSC channels, including the subchannels. You can also stream MP3's and JPEG's from a ViiV system (official line) or some 3rd party software products.
Yes, it does have some bugs in it still but it's a brand new receiver, both hardware and software. It's not based on the R15, so it's basically a start from scratch receiver. Looking back IMHO, the HR20 is a lot more stable then the 921 was when it first came out and the 622 has been out a lot longer and has the experiences from the earlier E* DVR's to help eliminate some of the bugs.