Federico Viticci's iOS 9: The MacStories Review, Created on iPad is both a comprehensive review and kind of a QA plan for iOS 9. 23 pages long!
Rene Ritchie's review is equally long but a bit breezier, iOS 9 review.
If you want something shorter, Jason Snell does a good job pointing out new features on the iPad including, Slide Over, Split View, Picture in Picture, Keyboard shortcuts and my favorite, trackpad support in the software keyboard.
These quick articles have some useful tips:
Here's a review of the new News app, Apple’s iOS 9 News App Review: Broken News. I tried it for a few minutes and gave up. The review lists alternatives at the bottom and I'm a happy user of Reeder backed by Feedly and I use NYT Now and occasionally I look at Nuzzle