Try the following:
Sub CheckWS()
Dim Sheet1rng, Sheet2rng As Range
Set Sheet1rng = Worksheets("Sheet1").UsedRange
Set Sheet2rng = Worksheets("Sheet2").UsedRange
For cell = 1 To Sheet1rng.Cells.Count
If Sheet1rng(cell) <> Worksheets("Sheet2").Range(Sheet1rng(cell).Address) Then Sheet1rng(cell).Interior.ColorIndex = 3
Next cell
For cell = 1 To Sheet2rng.Cells.Count
If Sheet2rng(cell) <> Worksheets("Sheet1").Range(Sheet2rng(cell).Address) Then Worksheets("Sheet1").Range(Sheet2rng(cell).Address).Interior.ColorIndex = 3
Next cell
End Sub
It will highlight in red all the cells on Sheet1 that are not equal to cells on Sheet2.