Have they? If anything, I think they have improved. It might not please everyone (I miss the old WoW), but it seems to me that Blizzard is making informed game design decisions based on what the users want. I wouldn't surprised me to hear they invested a lot in big data analytics.
Their big screw-up is perhaps the Diablo III auction house. The idea is good, but it has spiraled out of control. The auction house is now the only viable way to acquire gear. Playing only serves to rack money, but reselling is as good a way to make money. Gear serves to play, to rack more money, to buy better gear. The auction house is now the game. You can do very well at the game without ever playing the "real" game. Not to mention that shelling a few euros on the real money auction house will save tens of hours of farming, and real money continues to appreciate wrt in-game currency.
They've grown to include wider appeal and be more profitable.
Since the merger, Blizzard has aggressively moved towards in-game real money transactions including one high profile fuckup where they irreparably ruined the economy of an entire game, ruining the game itself for many players (especially their older and more devoted fans).
They've scrapped their major next MMO, pushing it back and folding much of the staff into other projects while this one goes back to the drawing board.
They predictably released StarCraft 1.5, the graphics update, but StarCraft is a known commodity and they didn't have the leeway to make substantial changes without massively disrupting the playerbase.
I can't find a single product of theirs that screams character and love and devotion to video games like their classics do, but every single product does appear to be a financially calculated move to extract as much money as possible from gamers.
From this long time (and no longer) Blizzard fan, modern Blizzard looks more like Zynga than the company they once were. More interested in ARPU than making wonderful games.
Speaking of love of and devotion to games, if you want to see what the original Diablo team has done lately take a look at Torchlight II - it still has that something that D3 is missing and D1/2 had.
Depends on your definition of "user". Diablo III was a huge let down to most of us who are fans of DII. It's not just the AH either; online always, crap gear, crap story, dumbed down skills, pay-to-win RMAH, and constant nerfs of a game that is not meant to be an esport. Bleh.
I'm the other way around: I bought it for the singleplayer campaign. It was terrible: short, half-assed, and boring. Huge contrast to the WoL campaign.
SC2 wasn't really designed for the single player campaign. Neither was brood war, Warcraft 1, 2, or 3. This genre of games has always been about the multiplayer aspect. The campaigns are nice add ons but not the core of the games.
I think you may be a tad misinformed. Even though the multiplayer aspect is very popular, Blizzard as a company has been known for really caring about the underlying story in both franchises. So no, the campaigns - which are the main tool used to advance the stories - are not supposed to be "nice add-ons."
Their big screw-up is perhaps the Diablo III auction house. The idea is good, but it has spiraled out of control. The auction house is now the only viable way to acquire gear. Playing only serves to rack money, but reselling is as good a way to make money. Gear serves to play, to rack more money, to buy better gear. The auction house is now the game. You can do very well at the game without ever playing the "real" game. Not to mention that shelling a few euros on the real money auction house will save tens of hours of farming, and real money continues to appreciate wrt in-game currency.