The fingerprint sensor in the 5S is interesting, but I wonder how accurate it will be in the real world; on top of that, with all the NSA news, I'm not particularly keen on Apple reading my fingerprint all the time. Supposedly, applications don't have access to it and it's not stored in the cloud, but I have little to no trust for companies.
The biggest news for me is the fact that the iPhone 5S has a new chip - the A7 - which has the honour of being the first 64bit chip inside a smartphone. iOS7 and first party Apple applications are all 64bit, and Xcode obviously supports it. While this obviously future-proofs the platform for more RAM, I wonder what other motives are involved here. ARM desktops and laptops, perhaps?
I doubt 64bit will provide much benefit today, but you have to hand it to Apple: at least they're done with the transition before it's even needed.