You knew the game required an internet connection when you bought it. The game isn't singleplayer so why are there some many very ignorant people saying that? This is a MULTIPLAYER game with the option to solo. It connects the same way as a MP game but then just don't let other players join the game. So I say again D3 is a MP game.
So your complaints about lag in singleplayer are wrong. There is no singleplayer. Get over it. It's not like other Diabos. I know you want it to be singleplayer but it just isn't so. So get over it and stop your whining. You are having LAG? You must have unstable internet.
Download/upload speed means nothing. The speed of your internet has nothing to do with the quality of your internet. For Diablo 3 you need QUALITY internet. If you didn't want to deal with this issue then why did you buy it? It clearly says right on the back of the box on the bottom "internet connection required". So your internet isn't as good as you thought. How is that blizzards fault?
I am on the east coast and playing just fine with latency of 150ms and with traffic shaping software I can get it down to 100ms. So all of you that are saying that the people playing without problems must be on the west coast are COMPLETELY WRONG. STFU and get out.
Nobody cares about your complaints. Complaining isn't getting you anywhere especially because you knew what you were getting into when you bought D3. Hell half of you probably have spyware sapping your connection without even knowing it. So your internet isn't as good as you've been fooled into thinking by your ISP so you blame it on Blizzard, is that it? I say again STFU and get out. Your internet isn't good enough end of story.