set sh1 = Workbooks(1).Worksheets(1)
set sh2 = Workbooks(2).Worksheets(1)
sh1.copy
sh2.cells.copy
Activesheet.Cells.PasteSpecial paste:=Values, operation:=xlSubtract
You could repeat for each matching sheet or reverse which sheet is
subtracted to get the correct "sense" of the difference (positive or
negative changes).