The only review of the iPhone 5S you'll need to read - AnandTech's.
At the end of the day, if you prefer iOS for your smartphone - the iPhone 5s won't disappoint. In many ways it's an evolutionary improvement over the iPhone 5, but in others it is a significant step forward. What Apple's silicon teams have been doing for these past couple of years has really started to pay off. From a CPU and GPU standpoint, the 5s is probably the most futureproof of any iPhone ever launched. As much as it pains me to use the word futureproof, if you are one of those people who likes to hold onto their device for a while - the 5s is as good a starting point as any.
It's a crazy world where the future of Apple becomes apparent not in its software, but in its hardware. The 5S looks like a significant step forward, and in my view, hints at a future where Apple's laptops and maybe even desktops will be powered by ARM, not x86. If I had the spare cash, I'd plonk it down for a 5S in a heartbeat - as it stands now, I have no way of testing iOS 7 myself.