I always thought they were great. But always overrated. They're massive communities are what helps make the games fun, and imo better than they are from a mechanic standpoint imo. (See Star Craft And War Craft Franchise. I consider Total Annihlation Superior) . And Diablo was a fun little game, but nothing earth shattering to me.
They support their games long after release by making pathes etc. Where other communities die.
The most annoying thing for me is that they made. WoW... and I hate MMO's (which is why) and they've been mostly developing the WoW unieverse. Instead of working on other IP's, but I don't blame them for it, it was the correct business decision obviosly.
Now Starcraft 2, was a fun little game as well. Probably not as good as starcraft BW, but not far off. And the original starcraft wasn't that balanced when it was first released either
But they've always taken forever to put out games... and never put out starcraft ghost... so heh, they're mostly the same quality-wise to me. They're just doing more MMO'ish things.