I'm loving this. I spend more time watching host intros and supplemental features than the films ha ha.
As far as quality goes, sometimes it does take a bit to get up to full res. I am on the new Fire TV, the one with 4K support, so things are pretty good for the most part. I have a friend with a first gen fire tv who says it's nearly unwatchable at times. Sounds like their compatibility testing was poor, and lower memory devices suffer. I'm not surprised there are memory issues with all the transitions and background images it loads.
Hopefully they get all the app kinks out.