Anybody who has started a video recording with their iPhone or iPad and promptly decided to switch from portrait orientation to landscape (or vice-versa), has found upon replay that the orientation didn't change, resulting in the majority of the video being sideways. Even though everything looks fine during the recording process, it doesn't translate to the finished product - an issue that Apple perhaps will address at some point.
iOS 10 brings several significant changes to the Photos app, including the addition of two new folders: People and Places. With its new facial and object recognition capabilities, Photos uses "Siri intelligence" to scan through your photos and tag them based on the content. This allows you to search for similar objects and people, so for example, you can now search your photos for, say, "car" and you should be presented with all of your photos containing cars (and likely a few that don't).
One of iOS 10's new additions to the Photos app is the Memories feature, which basically assembles photos into short videos based on time periods or locations. It will also create memories of holidays from your home country. If you don't want this for any reason, you can turn off this option by heading to Settings -> Photos & Camera and toggling off the "Show Holiday Events" option.
Starting with iOS 10, the Photos app attempts to identify and group photos of people who it thinks are the same person. It doesn't always get everything right however, and you might see that you have two different groups of photos that are actually the same person. This is an easy fix, you can either identify the photos as the same person, in which case it will ask you if you want to merge the photos, or you can use the "Merge" option.
The People album contains collections of photos sorted by the individual person, which makes it easy to find pictures of friends and family. It will, however, identify and group just about every face found in your iPhone's photos, including strangers in the background. While you can hide people that you don't want at all, you can also tag people as favorites and then have your People album only show your favorites. There are two ways to tag somebody as a favorite.