However with the release of iOS 8, many users started reporting a slight delay or lag in animation and UI transitions, making them wait until an animation has ended then they were allowed to interact and perform their tasks. To demonstrate this "lag", William Van Hecke decided to make a comparison video showing off an iPhone 6 running iOS 8 versus an iPhone 3G(S) running iOS 3.
Check out iOS 8 VS iOS 3: Animation Speed.