The only issue I found with the upgrade is most features come as turned on, I had to turn off a bunch if stuff to make it better.

So I went through it, disabled a bunch of useless features and I cleared out old applications/voicemails/textmessages/3,000+ unread emails and it is better now. There is still some lag, but there is no 15+ second lag in between typing a message to someone and having it appear on the screen. Disabling that icloud feature really helped.