A question on your rating system

For the most part regular series and movies are reasonably good and giving a good report on the quality of the show. My question is why do some of the shows (ex: The War Between the Land and the Sea, not meaning to put down the show) has a high rating.  I watched the first episode and found the quality to be little more that "B" level, not that i don't like B movies. For some reason its' rating is like 6.7.  Now I compare this to a Theater Release movie and has actors like Mel Gibson in it and it gets a rating like 5.1 (hypothetically).  I actually enjoyed the Theater release movie, but, could barely keep my eyes open for the B level show.  Now I see like 15000 people have rated these show so by all rights it should be reasonable accurate.  Now I don't consider myself to be a critic, but i do have a good understand of acting quality, directorship and writing ability.  (fyi I have university training in English Literature).  I am also old and don't grammer check anymore. :-)  

My question is how could such a poor quality show (I would rate about a 4.8) gets such a ridiculous rating of 6.7?