In terms of overall improvement over iOS 6, 7 out of 10.
My quick summary is that iOS 7 is a working progress. User interface changes aside, iOS 7 is about as major upgrade as iOS 6, which wasn't as big of an upgrade as past major iOS updates were.
Having said that, iOS 7 brings smaller but very useful and important changes, such as Control Center, call and message block, audio-only FaceTime, improved usability on Safari (combined address/search bar, quicker access to iCloud tabs and private mode), Today view on Notification Center, smart inboxes in Mail, dramatically faster App Store, and cellular data provisioning per app.
My past scores:
iOS 1: 10
iOS 2: 10 (most important new features: App Store)
iOS 3: 6 (most important new features: clipboard, MMS)
iOS 4: 8 (most important new features: multitasking)
iOS 5: 9 (most important new features: iCloud, notification center, iMessage)
iOS 6: 6 (most important new features: Maps, Siri)