The big question about any OS upgrade is, will installing it make you glad you did?
The answer for iOS 6 is yes, but some users answer yes more emphatically than others.
The two biggest changes to iOS 6 are Maps and Siri. It's easy to jeer at the former, and Maps certainly has its problems, but it is an excellent choice for in-car turn-by-turn. Siri continues to improve and is now heading towards becoming an essential component of iOS rather than a gimmick.
Do Not Disturb, despite its lack of scheduling granularity, is a triumph. Apple certainly didn't get there first with this feature, but we're sure glad the company got there eventually.
Elsewhere, we liked that Apple's continuing to work with strong foundations and, generally, improving things. Relatively minor updates to Mail, Safari, Camera, Photo Stream, Phone, Share sheets, Find My iPhone and privacy all add up to a big improvement overall.
There's no getting away from iOS 6's differences across devices. In some cases, hardware limitations must be to blame, but some feature cuts appear arbitrary and driven by Apple wanting users to upgrade. For example, the iPhone 4's inability to make FaceTime calls over 3G is baffling, considering it works with Wi-Fi.
Elsewhere, Maps isn't good enough in all use cases, and it really should have been, while Passbook is a nice app that has poor support, and some of Apple's design decisions have been questionable. We can put up with the status bar changing colour, but the awkward search and cropped names in all iOS stores are bad to the point of putting you off searching for and buying things.
We could say the same about iOS 6 as we did about iOS 5: it "has been trailed for so long that the element of surprise went ages ago, but there's enough here to make your iPhone, iPad or iPod touch feel shiny and new all over again."
iOS 6 is rather like the iPhone 5 or OS X Mountain Lion - the refinement of something that already works extremely well. Apple isn't overhauling things for the sake of it but, in the main, making the iOS experience gradually better. That in itself is something other companies would do well to emulate.