If you think something wrong, take it into a apple store, if you are within your year, they will help.
Yeah its instant. I just really liked the softer touch of the 4S.Is the response time good Chetan? That would be my primary concern. You can always get used to the feel if it is functioning properly.
It might loosen up. I never noticed a difference from what I recall but that was almost a year ago too.
The iPhone 5 home button has more of a "click" to it. Which isn't an accident.