My opinion is that there's no 'objective' quality, but certain opinions may get you laughed out of serious circles! I think broad consensus over quality could be as close as one gets to objective quality, but you can always find a dissenter (I'm sure you could find someone to argue that Lord of the Rings is hideously overrated and unsuited to Tolkien's story, or that John Williams' classical influences sink the artistic credibility of Star Wars and his other works). For me, I'd say that you can't boil down a work and find a molecule of quality, it's all taste and opinion, even as certain works are designed to appeal broadly.

Hell, quality itself can be a slippery thing to define. Few would argue that, to go to Williams again, War of the Worlds is a bad score, but you can definitely find a range of opinions as to how it fares outside of the film (I like it, but definitely hover over 'skip' at times). For something more divisive, I love Joker and think it's a stunning and brilliant work in and out of context, but you have many here who would vehemently disagree!

(As far as poor performances, I'm not sure even that makes a work bad. Possibly harms its potential impact for some listeners. For example, Godzilla (54) is a brilliant score, but it can be hard to listen to out of context for its notoriously muffled and restricted mono sound. I would still say it's "objectively" a great score even in that form! [Also someone please rerecord that full score please.])

Well, that was a ramble!