For future phones and tablets, seamless updates (borrowed from Chrome OS) mean download and installation will take place in the background, and you'll only need to reboot once they're complete.
Oh, and reboots after applying updates shouldn't take longer than usual thanks to that pesky "Android is upgrading" and "Optimizing apps" screen finally being killed by the brand new JIT compiler. This also helps cut down app installation and update times compared to Marshmallow - and that's an improvement you're bound to see from day one, especially on devices that historically struggled with such a workflow (the Nexus 9 comes to mind here).
While the seamless update process can't be implemented on current phones and tablets for technical reasons, the rest of the functions described here are available for all devices running Nougat.
Android 7.0 comes with a new graphics API called Vulkan, which should enable much better 3D game graphics on devices with powerful enough hardware to support it. The latest version of the OS also has a built-in Virtual Reality mode, which will only be visible on Daydream-ready devices, this being Google's new grand VR push. Expect to see Daydream-certified handsets as well as a Google-made Daydream VR headset to put your phone into by the end of the year.
With Direct Boot, essential services start running even before you enter your password when you turn your device on. So you'll get notifications and hear alarms as soon as possible. Finally, with file-based encryption, your files are better isolated and protected than they were in the past with block-level encryption. However, only devices launching with Nougat on board will get Direct Boot and file-based encryption by default. For those who update to Android 7.0, the choice to switch to file-based encryption is available in Developer options, but doing this requires a full wipe of all your data, so we'd guess it's not something most people will even consider.