Let's look at that.
2007: iPhone.
2008: iPhone 3G. Same phone but with 3G.
2009: iPhone 3GS. Same as 3G but a bit faster.
2010: iPhone 4. New case, retina display, faster etc.
2011: iPhone 4S. Faster, better camera and Siri.
2012: iPhone 5. Faster, new case, bigger screen.
2013: iPhone 4s. Faster, Touch ID, better camera.
It's hard to say any of those releases were revolutionary except the original iPhone. All since has been steady improvement. And that's a good thing.