Blizzard used to make some quality games. Both the blizzard north and blizzard teams.
This is just my, possibly unpopular and also likely cliché opinion. But I blame world of Warcraft and Activision. WoW gave them ridiculous amounts of money and Activision gave them Uhhhh...'corporate refinement' that combination led to them becoming much like most other big name game companies. Money over fun. It's sad...but it is what it is.
Again, that's just my opinion, i'm sure lots of people have enjoyed post Warcraft 3 blizzard games, but for me, that was their last one where gameplay came before profit.
When people talk about Diablo 2, they are always referring to the version including the expansion.