It's been very popular to hate on WoW for a long time. Many people complaining haven't played the game for years as indicated by them complaining about issues that haven't been in the game for a long time.

Of course there are a lot of valid complaints too, like the plot in WoW for those who care about the story in a MMO.

Despite all the doom and gloom you might've read over the years, the sold copies of the expansions have been increasing and while I'm under no illusion that the player count is anywhere near the peak of what it was, it's far from "going downhill".

As for wether it's "worth it or not", is very much subjective to what you are looking for in a MMO. WoW has it's strenghts and weaknesses, and if what you're looking for is one of it's strenghts like tab target combat or competitive end game content, then yes, it's absolutely worth it.

If you're looking for a MMO that is more focused on the story, or other systems like player housing, or more profession focus, then no, it's probably not worth it for you.