I wouldn't call this the WORST expansion, but clearly, they missed the mark on opportunities.
Story - The story was too edge-lord that it honestly made DKs look dainty in comparison. This was an excuse for Sylvanas redemption arc and that is about it. Although the covenant campaigns were brilliant and amazing to follow, time gating destroyed the fun in them.
Features - As expected, there were core expansion features such as Torghast, Covenants, and Soul Binds...however, the restricting aspects really hindered the systems. We get a feel from the developers that "you should just keep playing and eventually you get our vision" dev visions should be out of the box obvious not something players should work toward.
Graphics/Zones - While each zone was centered around color schemes they were truly breathtaking.
Overall Blizz did fix a majority of the issues toward the end of the expansion, but it certainly won't be missed by this player.