FitzTheRuke
Legend
I would agree that there is a negative vibe in online discussions the last couple of years. The forumite "zeitgeist", but that doesn't seem to hold up when Iooking at the actual products themselves the last couple of years, or look at their sales numbers in the slices of data that are available.
There's another thing that factors in to how I get my "gut" feeling (and I trust my gut, it's rarely wrong) that the products have been lacking. (And I think you're right, not only is there no objective way to really judge these things, but if you try, I think that you can only conclude that there's no real drop in quality, at least not a substantial one). That is, that for US (my FLGS) there has been a fairly substantial drop in sales on Adventure books. This factor inevitably deflates my feelings on the state of things.
Of course, there are many reasons for that beyond quality. In no particular order, they are: A new "edition" is coming, which makes customers shy of new products; there is and must be some success on WotC's part in getting people to switch to DDB (or physical/digital bundles sold through DDB); customers are generally overwhelmed with Adventure products (IE they already possess more adventures than they can run & books that they still mean to "get to" on their shelves); justly or unjustly, many reviews of recent books do not do a lot to push people toward buying them; Spelljammer sold fine, but was nearly universally disappointing, which colors folk's opinions of things that come after. I could probably go on.
The "overwhelmed shelves" is probably the biggest factor for a small FLGS. Unlike, say Amazon (or WotC overall) we rely on a smaller group of regular customers buying more things. This would explain why the Core books are still selling okay, while the Adventures are slower. There's still a LOT of people "just getting into D&D". These people wouldn't really know what to do with an Adventure (yet). But our core customers have slowed down getting "everything". Therefore, core sales have dropped and we're down to (relatively) a book here, a book there.