Mission Control is the new Mac command center included with OS X Lion. Mission Control lets you work with Expose, Dashboard, Spaces, and full-screen apps in a single easy-to-use interface. That means you get a bird's-eye view of what's happening on your Mac with just a gesture or a mouse click. Mission Control displays all open windows and applications, just as Expose does in Snow Leopard. But in addition, Mission Control also displays all of the desktop Spaces you create, provides Dashboard access, and displays all currently running full-screen apps in a row of thumbnail icons across the top of the Mission Control display.
Want to move to a different desktop Space? Just click its thumbnail. You can move between open apps and windows the same way. But Mission Control does more than just let you easily move around your work environment. It also lets you add or remove desktop Spaces. Creating a new desktop Space is as easy as dragging an app to the top row of Mission Control. Add more apps to the new desktop Space, and you're ready to go.
Mission Control simplifies the process of working with multiple apps, windows, and Spaces, while retaining all the functionality of Expose. I think Mission Control is going to be a hit with Lion power users.