The Killing is pretty reviled among critics so they're definitely not bringing it back for quality/critical acclaim.
The critics are no objective arbitor of quality and no one has said that season 2 (at least) was a "critical" success.
But AMC sure as heck wouldn't give it another go unless they thought there was a fair amount of quality there -- and considering this network's track record with one hour dramas, I'd say they are at least as good judges of quality as the critics if not considerably better.
Networks don't keep shows on just because they think it's good. That simply doesn't happen. If it has CRITICAL acclaim then it might be kept on, especially if the channel is interested in that (i.e. HBO). There's nothing wrong with liking the show but to say that it's seen as high quality is simply incorrect.
Plenty apparently see it as high quality, suggesting YOU are incorrect. All I did was type in THE KILLING and RAVES and the following is the first thing that came up:
(that's for s1)
for those who don't like clicking,
it had 29 positive reviews from real critics, no fair and no bad
it had 52 positive from viewers, 10 fair & 10 bad. The first comment on the viewer side say, "the critics have it right this time."
Majority rules is no barometer of artistic success -- all you have to do is look at what makes money in theaters. But dismissing the show because it is a trendy thing to do is just as bad as thinking 'if it is trek it must be good' or 'AVATAR made so much it has to be as great as folks say.'