I've had this argument with my (tending towards elderly) parents while introducing them to Netflix. They don't understand rating for enjoyment, and keep rating for "quality". They'll watch a show, absolutely hate it, but give it a 4 or 5 star rating because "it was well produced and the camera work was good, but it isn't the sort of thing I personally like to watch".

I'm worried about the thumbs up/down, as Netflix has increasingly recommended shows I do not like this year, and I don't think the thumbs solves the "rating for perceived quality" issue. I've been using Movielens for recommendations a lot instead, and it seems more accurate for me... and it has enough stats to show that on their site, most rating is not binary, much closer to a normal curve for average movies or a linear graph on really good movies. (It lets you see the distribution curve on individual movies, and other metrics.)