The following PowerShell script will get the patch level of your farm:

   1: #gets the build string for a SP2010 FARM
   2: Set-ExecutionPolicy Unrestricted
   3: Add-pssnapin microsoft.sharepoint.powershell -EA silentlycontinue
   4:  
   5: $farm = Get-SPFarm
   6: $version = $farm.buildversion
   7: $version