Yeah they aren't as sensitive as previous capacitive buttons. Not sure if it's by design or a flaw. In any event, I've notice that my touch has to be more specific and deliberate that what I thought. I would casually tap it with the side of my thumb but if I really look, I would see that my thumb isn't really tapping the button or not putting enough pressure. Over the last week, I've gotten use to it and don't have any issues. Guess I just learned my device LOL. Anyhow, there are several threads about it and maybe they would be better served to help you.
Yes I have noticed a delay as well I thought it might have been due to my protective screen which it could still be some. But looks like there a update rolling out if you get Updates Make Sure to let folks know what Carrier your with.