You can shit all over their products all you want, but you can't name a single competitor with more success in any of the respective genres (with the exception of HotS, but even Dota has a fraction of LoL's popularity).
Considering the amount of money I gave Blizzard in the last 15 years or more, no I'm not shitting on their products, I'm criticizing them (for what is worth, so almost nothing) for delivering products that keep taking distance from their original design, which I loved more. I'm not alone in having something to say about WoD, yet I played it for 3 or 4 months, I played D3 for hundreds of hours, the rest of their offers are not matching my taste, but I don't dispute they can and do make awesome games.
As someone on these very forums said: I bitch because I care. See, I love WoW, I have over 1000 levels on 11 different characters, so yeah, I played WoD too for a good while, but I still think it's not a long lasting xpack and it's not as good as the previous ones. Even Cata is better from my point of view.
I would be the first to rejoice if the next xpack is awesome and addicting. Diablo is a game I spend a little time every now and then, it's now better than it was at release and for this I'm grateful, I don't give enough of a fuck about it tho. My heart is with WoW and WoW is worse now in my opinion and apparently the opinion of another 3 million players, plus soon the banned botters. I found solace in FFXIV for my MMO needs and it may even last me a long time (alongside my secret addiction for GW2), but I love WoW and it pains me that WoD is such a mediocre expansion.
Competition? I don't think Blizzard has much competition in terms of numbers, but I don't think either that other games can't be equally good, maybe they are not everyone's taste, but some are top quality nonetheless.
EDIT: Smed, the only change worth mentioning, instead of attention whoring, would be to tell us that a great game is coming out. Everything else is bullshit.