Update October 21 2015: iOS 9.1 has now been released. View the changelog for all the details.
Here is a brief look at what to expect, and come back for a full look at all the changes when iOS 9.1 is released in the coming weeks or months.
A range of new weather emojis will allow you to keep your friends updated with more specific emoji-weather-forecasts.
These older characters have retro-actively been deemed worthy of a colorful "emoji presentation", although until now mostly stuck with their black and white text-presentation.
It's great to see Apple double-down on what appears will be the first operating system to include every single emoji in the Unicode Standard1.
Above: Unicode 7 emoji images from iOS 9.1
More details will come in a separate article, closer to the public release of iOS 9.1. In the meantime, fire up the fast search feature on Emojipedia, and see if there's something coming for you.
iOS 9.0 is scheduled to be released on September 16, and includes a range of new emoji flags.
iOS 9.1 (the update that includes all these changes) does not yet have a public release date, but is likely to be in October or November 2015.