You are given the option to choose between a background color or to use Muzei content provider integration to have dynamic wallpaper. The second option allows you to have your favorite photos as a background or to select one of many extensions to provide beautiful wallpaper from many different sources.
Complications come in two forms, first, you have the option to enable:
• Watch Battery
• Phone Battery
The second are 3rd-party complications in the form of DashClock API extensions. This option allows you to use any extension as a complication. This complication can be further configured to show or hide each individual part (icon, title, status).
I love being able to customize my watch face! Really nice integration!