Root directory access is poor, ability to control the file is poor, can't stop/start without going back to the beginning, the adverts are annoying but not too bad if I am honest. This is not iOS standard. And gives Kindle Fire HD a bad name! Do yourself a favour Amazon. Control the quality of the Apps or you will lose customers.
Doesn't work too well on my Kobo Arc - two or thee times during a film it will stop with the error message "cannot be played". But it can - i just have to reload the movie. Also, it doesn't "remember" where I left off if I have to stop viewing in the middle of a movie.