With mission control you can view all applications and all screens at once.
Not really - the small thumbnails at the top are hardly big enough for me to tell what's in it, and it's difficult to tell which of the thumbnails is the one I'm currently on. Spaces allowed you to see all desktops in the same size, with the other desktops surrounding it in a relative way. In Mission Control, the active desktop is always in the middle of the screen, regardless of which one it is, making it difficult to know which one it is, and the other desktops appear at the top of the screen, discriminating between the active desktop and the others. In Spaces you could, in 2 steps (activate Spaces then activate Exposé) see ALL your windows in the same size. There is no way to do that in Mission Control: the apps on non-current desktops are not exposé-d and they are much too small to see anyway.