Gotta say...a little disappointing. I watched a show that I normally watch over DirecTV with very good video and sound quality. Nat Geo's video quality on the aTV was just marginal and audio was only 2-channel. Gonna have to do better than that for me to switch from DirecTV to aTV.
Have a legacy Apple TV here and wish the newer iOS models had local storage options so I wouldn't have to use my Mac or my iPhone to listen to my music library which is the best saving grace of my old 160GB model
As far as your experience with Nat Geo on the iOS Apple TV, you're not alone with that experience. On my Roku box which has native support for Dolby Digital and the works, Nat Geo is the same awful experience despite the channel/app having far more potential for any streaming platform.
Other services for streaming content such as History/H2 don't even support my cable provider so I have no means of watching many of my favorite networks.