I have downloaded a lot of 3D movies, they are all SBS - L/R or Top/Bottom. If you want frame packed full 3D you need to get the Blu-ray of the movie. On my active 3D system these SBS are lower resolution than Blu-ray but the quality is always fine. Since there is a sweet spot that looks good then my guess is your set is the problem and not the movie. If it looked bad from every angle I'd say you have a crap file.
What is you TV set make/model?