I have to agree, the DirectTV Now app is probably the worst streaming app that I've ever experienced since I started to use Apple TVs ten years ago.
The content is fine (actually quite good), but the functioning and reliability of the app and service is an outright disgrace. Some of the real-time content (local TV stations) works fairly well, but the overall UI is very poor and the on-demand services (HBO, TCM) are so buggy as to be little more than a complete frustration and time waster.
The fact that this has (apparently) been going on for more than a year leaves me little hope that it will ever be fixed (unless they start over with a completely new code base and infrastructure, with new management and a restructured engineering team).
I've had the service for about 3 months and if I had to pay more than the $10 I got as a part of a deal from AT&T then I would have cancelled it after the first few weeks.