Yes, but this is exactly the definition of being subjectively. As you say: it is peoples OPINION. That does not make it objective at all. Objectively would be a statement like "on FOTD they changed more into an AC/DC direction and used more repetition than on previous albums", or "the guitar sound has less mids and treble than on SIT", because those are measurable facts. As soon as you add "and that's good / bad" or a rating, it is not objective anymore, but simply a personal taste.
Proof how subjective it is: I think Weekend Warrior is a great track, and even without he title track, FOTD would still be a good album. It is just a matter of opinion.
Since I consider Doom Metal the greatest of all Metal subgenres, "dark and monotonous" can be a very good thing.