It seems to me that the solution should be to just make Mission Control an optional and additional feature. Leave the old spaces and expose intact. As for grid view in spaces, this should be no problem. Spaces are still numbered in grid view and so the linear translation in Mission Control would just follow that.
It's the fact that Apple is forcing this on us that is mind boggling. I know a lot of people rant about Spaces, but I'm more astonished with how bad Mission Control messed up all-window expose. The entire point of pressing the expose button as it stands is to "un-layer" and tile your windows. Now, however, if you have two windows of the same application open (in addition to others) pressing the Mission Control button will actually force layer the windows of the same app together! Mission Control actually does the exact opposite of the solution expose provided and yet it's a "replacement" for expose! Madness...
Hello. Lion still has expose with the grid layout. You just have to enable it. I too was frustrated with the layering of windows in mission control, but now that I enabled expose, I love mission control. To see your windows in a grid, you swipe down; to see a row of linear spaces across the top of your window and your open app windows stacked/layered on the desktop, swipe up. I love Lion.