When the first iPhone came out (basically the i8), it was innovative, but the following generations were still revolutions because the tech was still fairly immature at the time. The S5 (basically the 911), while still an improved product from its predecessor, is just a fairly basic upgrade from the S4. The tech is more mature and they're basically refining at this point.
I agree with likening the i8 to the original iPhone but if that is true then the 991 should have been the Nokia 6210 a brilliant phone but devoid of all the tech present in the iPhone.