The problem with the up/down system for me is not my own ability to like/dislike specific titles, but more the fact that Netflix no longer displays the average of all user votes. Sure different people used the 5 star system in different ways, and there were some who may have misused it by giving poor ratings to things they never intended on watching, but it was a great signal to me for the extremes.

Scenario: I'm considering some odd looking sci-fi movie to watch that I never heard of before. Ratings between 2-4 stars might not tell me much, but very reliably titles with only one star were terrible movies. Now Netflix happily recommends any and all sci-fi titles, saying they are a "98% match" for me! Sure by category, but when the movie is a low budget dumpster fire I no longer have that instant signaling that the previous rating system gave me.