iOS 7 now allows for the automatic downloading of app updates in the background, which is convenient for users who have a lot of apps installed on their iPad or iPhone. The downside to these automatic updates is that developers sometimes roll out a major overhaul to an app that takes a user by surprise. Even someone experienced as me can be taken aback for a few moments when an app icon changes or a UI is completely different.
If you have automatic updates turned on and want to find out what apps were recently updated, you can find this information easily in the App Store app. Just open the App Store app and tap on the "Updates" button on the right-hand side of the bottom bar. You will then see a list of all recent app updates. Tap on the "What's New" link to view the changelog, which lists all the new features and other changes the developer made.
You can turn on automatic updates using these instructions.