Diablo 3 was a disappointment at release due to the always online requirement (which was rare back then), the ultra boring campaign, real-money auction house, and no end game.

Diablo 3's expansion though fixed all of those mistakes set a solid foundation. It was very good for several years. But then they stopped developing it, presumably (hopefully) because they started to pour all their resources into Diablo 4... which I have high hopes for, but with Path of Exile 2 on the horizon, I'm not going to be too disappointed if it flops.