void Main()
{
    string fileName = @"c:\path\to\my\file.xlsx";

    using (FileStream fs = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
    {
        using (SpreadsheetDocument doc = SpreadsheetDocument.Open(fs, false))
        {
            WorkbookPart workbookPart = doc.WorkbookPart;
            SharedStringTablePart sstpart = workbookPart.GetPartsOfType<SharedStringTablePart>().First();
            SharedStringTable sst = sstpart.SharedStringTable;

            WorksheetPart worksheetPart = workbookPart.WorksheetParts.First();
            Worksheet sheet = worksheetPart.Worksheet;

            var cells = sheet.Descendants<Cell>();
            var rows = sheet.Descendants<Row>();

            Console.WriteLine("Row count = {0}", rows.LongCount());
            Console.WriteLine("Cell count = {0}", cells.LongCount());

            // One way: go through each cell in the sheet
            foreach (Cell cell in cells)
            {
                if ((cell.DataType != null) && (cell.DataType == CellValues.SharedString))
                {
                    int ssid = int.Parse(cell.CellValue.Text);
                    string str = sst.ChildElements[ssid].InnerText;
                    Console.WriteLine("Shared string {0}: {1}", ssid, str);
                }
                else if (cell.CellValue != null)
                {
                    Console.WriteLine("Cell contents: {0}", cell.CellValue.Text);
                }
             }

             // Or... via each row
             foreach (Row row in rows)
             {
                 foreach (Cell c in row.Elements<Cell>())
                 {
                     if ((c.DataType != null) && (c.DataType ==           CellValues.SharedString))
                     {
                         int ssid = int.Parse(c.CellValue.Text);
                         string str = sst.ChildElements[ssid].InnerText;
                         Console.WriteLine("Shared string {0}: {1}", ssid, str);
                     }
                     else if (c.CellValue != null)
                     {
                         Console.WriteLine("Cell contents: {0}", c.CellValue.Text);
                     }
                 }
             }
         }
     }
 }