Google's "opinion" for better or worse is fact. Let's hope they figured out a way to differentiate between genuine bad reviews and those with underlying motives.
Even more, once you move to anything slightly controversial, an opinion can be genuine, meaning sincere, but still not valid for the person searching ("they sold me the movie I asked for but it had too much violence!").
Yes, just as with voting on HN -- does that downvote mean it's an inane comment, or just that someone disagrees?