Well I've had an iPhone since the 3 and I would say that Steve is probably rolling over in his grave with this update.
It's not that I don't like some of the changes. Built in flashlight it pretty neat. Individual app control over hardware buttons and functions are neat too. I like that the folder brings up a new windows - but damn you think they coulda fit more than 9 icons on the screen by shrinking them down a bit - I mean scrolling a folders window is just silly. The camera seems quicker to take a picture which is a plus with children.
What pisses me off - having to slide left to delete an email versus right.
What makes me happy - the option screen for when you choose what to do with an item (such as Photo) are much more expanded and it looks like you can attach more than one photo to an email.
My overall impression is that it somehow just isn't as pulled together as Steve's iOS was. Steve kept everything under control and kept it simple. Many complained that you couldn't tweak your phone enough - but he kept it simple for the laymen (ie: my 72 year old mom bought one and she figured it all out in no time - granted she is probably a bit better than most 70+ people on the computer, but I also gave my Dad an iPad mini for his 80th birthday and he's doing okay with it, and he just about knows where the power button is on the computer
).
My biggest concern is with the direction Apple is heading. I this they are going to try and make every customer happy and you see it already. There are more hardware versions available across the line than ever. The scope creep in hardware and software will make it harder to decide on what to do - and that will turn away the people that came to Apple in the first place for it's simplicity.
Now, on the flip side, I manage our Exchange and mobile messaging environment where I work so I get to trial many devices and lots of enterprise apps. I have to say that I've been working with the Samsung devices lately and the S4 is a damn impressive phone. I've been running an iPhone 4S (been saving my upgrade for the 5S for half a year), but when I go to the AT&T store if I am not blown away with improvements in the iPhone 5S I will very likely jump ship and switch to a Samsung S4 or S4 mini.