What fails most in BFA for me personally is the fact the successful systems are the success stories from previous expansions (like Mythic+).
The new features of BFA feel half-baked and are generally poorly executed. An example would be Warfronts, which was one of the big selling points of BFA. I haven't seen a single positive comment about it, and it truly baffles me this made it into the live game.
I still enjoy playing BFA, but much of my enjoyment is based on what older expansions brought to the table, with a bit of polish.
That being said, imo this is not even remotely as bad as things were in Warlords of Draenor, and a lot of the failed concepts can be largely avoided - they're not all mandatory in the same vein as garrisons were.
The art/design, lore/story, and audio/music teams have done an amazing job this expansion imo.