Of all the reviews that I’ve read so far, John Gruber has the best take on it over at Daring Fireball.
This part was particularly interesting:
I have only two bad things to say about 3D Touch. First, Apple missed an opportunity to borrow a great feature from Apple Watch. On Apple Watch, you can force touch in the notification list and you get an option to Clear All. 3D Touch has no effect in iOS 9’s notification list, and there remains no way to clear all notifications at once.
Downright lunacy there, Apple. Come on!