Oh boy yes, iOS 4 was a beast. My iPhone 4 on iOS 4 was an utterly-butterly experience!
Every OS from there was just a little further away from that.
iOS 5 fed my iPhone a few beers and made it hiccup now and then. It lost a little coordination but still could drive around, albeit a little slower and more cautiously.
iOS 6 was a bit of a meanie. iOS 6 tripped up my iPhone and broke its ankle. It was hobbling badly after that and never quite recovered.
iOS 7 pushed my poor little iPhone into a meat grinder, flicked the switch, and walked away. I had to say goodbye and buy a 5S