I've had iOS 7 beta on my iPhone 4S since days ago. I love it! It just exudes a sense of minimalist aesthetics overall, in my opinion. Well, maybe not that much love for the new app icons. I prefer the older ones for that matter.
There are bugs of cos', but they don't annoy me to the point that I'm complaining. The battery drains slightly faster now. I think it was much worse before I disabled Settings>General>Background App Refresh and Settings>iTunes App Stores>Automatic Downloads. Some apps crash upon opening, which is very expected as developers have not updated their apps to be compatible with this new iOS. Major apps such as Facebook (no notifications though?), Whatsapp, Instagram, Twitter and Viber are working as per normal. iMessage / SMS, FaceTime, Hotspot, Safari and location services are too. Oh, I can't zoom while recording video using the default camera app. Or is that not supposed to be working for the iPhone 4S yet?
Anyways, I won't go back to 6.1.3. iOS 7 beta is the closest thing I could get to having a jailbroken phone. Most of the Cydia tweaks I used (when on iOS 6.1) are already present in this new iOS. The only tweak I miss badly is f.lux. Overall, I'm very impressed with this considering it's only the first beta.