I have to disagree. Fifteen Million Merits is still my favorite episode, and what's more, I don't think it's about the intrusive ranking at all (meta-point: one of the best things about Black Mirror, IMO, is that people will often disagree on not only the quality of an episode, but what the episode was even about. That's how you know it's good).
I think the moral of that story was the inherent futility of ever rebelling against the System. Most people don't try, most who try fail, and even for the one-in-a-million who succeed, the System just instantly reconfigures itself to absorb your rebellion as part of it. Other works have done the "revolutionaries always become the new dictators" shtick, but Fifteen Million Merits did it better because it shows that this process doesn't even require a villain (like in, say, Animal Farm). Everyone in that episode, even the Simon Cowell stand-in, was just punching a clock and doing their job; the suppression of revolt was purely an emergent property of the system... as it usually is in real life.
It was the bleakest, most nihilist bit of television I think I've ever seen, made better by the fact that it wasn't empty "dark for dark's sake" like Twilight Zone-esque twist endings tend to be. I had to go for a walk afterward. I don't see how you can't like it... but like I said, the fact that people can disagree so profoundly is one of the show's best qualities, so I'll upvote you anyway and not hold it against you :)