If you’ve been using iOS for a few years, you might notice that Apple has tuned up system animations up a little in iOS 11. This is Apple saying it has a brand new animation library and want you to take notice.
Some people might find the animation annoying. Good thing is there is a setting for you to reduce the motion.
Goto Settings app > Accessibility > Reduce Motion and turn on the “Reduce Motion” switch. You will notice opening and closing apps are now almost instantaneous. Try it out, you might prefer the less motion setting.