reg query errorlevel, setlocal EnableDelayedExpansion, endlocal

If you use reg query and errorlevel then use !errorlevel! instead of %errorlevel%.
At the start of script write setlocal EnableDelayedExpansion and at the end write endlocal.

Whole code:

setlocal EnableDelayedExpansion
reg query HKLM\SOFTWARE\Wow6432Node > nul 2>&1
if !errorlevel!==0 echo 64-bit windows found
endlocal

If you need to find specific value then for the perfect situation you need to make two reg queries. One for key and second for value cause in situations when the key was not found you will get another errorlevel.
This is wrong:

setlocal EnableDelayedExpansion
reg query "HKCU\Software\Adobe\Adobe Acrobat\11.0\Originals" /v bDisplayAboutDialog > nul 2>&1
if !errorlevel!==0 echo found bDisplayAboutDialog
endlocal

This is good:

setlocal EnableDelayedExpansion
reg query "HKCU\Software\Adobe\Adobe Acrobat\11.0\Originals" > nul 2>&1
if !errorlevel!==0 (
reg query "HKCU\Software\Adobe\Adobe Acrobat\11.0\Originals" /v bDisplayAboutDialog > nul 2>&1
if !errorlevel!==0 echo found bDisplayAboutDialog
)
endlocal

Other error codes:

   0 ERROR_SUCCESS The action completed successfully.
  13 ERROR_INVALID_DATA The data is invalid.
  87 ERROR_INVALID_PARAMETER One of the parameters was invalid.
 120 ERROR_CALL_NOT_IMPLEMENTED This value is returned when a custom action attempts to call a function that cannot be called from custom actions. The function returns the value ERROR_CALL_NOT_IMPLEMENTED. Available beginning with Windows Installer version 3.0.
1259 ERROR_APPHELP_BLOCK If Windows Installer determines a product may be incompatible with the current operating system, it displays a dialog box informing the user and asking whether to try to install anyway. This error code is returned if the user chooses not to try the installation.
1601 ERROR_INSTALL_SERVICE_FAILURE The Windows Installer service could not be accessed. Contact your support personnel to verify that the Windows Installer service is properly registered.
1602 ERROR_INSTALL_USEREXIT The user cancels installation.
1603 ERROR_INSTALL_FAILURE A fatal error occurred during installation.
1604 ERROR_INSTALL_SUSPEND Installation suspended, incomplete.
1605 ERROR_UNKNOWN_PRODUCT This action is only valid for products that are currently installed.
1606 ERROR_UNKNOWN_FEATURE The feature identifier is not registered.
1607 ERROR_UNKNOWN_COMPONENT The component identifier is not registered.
1608 ERROR_UNKNOWN_PROPERTY This is an unknown property.
1609 ERROR_INVALID_HANDLE_STATE The handle is in an invalid state.
1610 ERROR_BAD_CONFIGURATION The configuration data for this product is corrupt. Contact your support personnel.
1611 ERROR_INDEX_ABSENT The component qualifier not present.
1612 ERROR_INSTALL_SOURCE_ABSENT The installation source for this product is not available. Verify that the source exists and that you can access it.
1613 ERROR_INSTALL_PACKAGE_VERSION This installation package cannot be installed by the Windows Installer service. You must install a Windows service pack that contains a newer version of the Windows Installer service.
1614 ERROR_PRODUCT_UNINSTALLED The product is uninstalled.
1615 ERROR_BAD_QUERY_SYNTAX The SQL query syntax is invalid or unsupported.
1616 ERROR_INVALID_FIELD The record field does not exist.
1618 ERROR_INSTALL_ALREADY_RUNNING Another installation is already in progress. Complete that installation before proceeding with this install.For information about the mutex, see _MSIExecute Mutex.
1619 ERROR_INSTALL_PACKAGE_OPEN_FAILED This installation package could not be opened. Verify that the package exists and is accessible, or contact the application vendor to verify that this is a valid Windows Installer package.
1620 ERROR_INSTALL_PACKAGE_INVALID This installation package could not be opened. Contact the application vendor to verify that this is a valid Windows Installer package.
1621 ERROR_INSTALL_UI_FAILURE There was an error starting the Windows Installer service user interface. Contact your support personnel.
1622 ERROR_INSTALL_LOG_FAILURE There was an error opening installation log file. Verify that the specified log file location exists and is writable.
1623 ERROR_INSTALL_LANGUAGE_UNSUPPORTED This language of this installation package is not supported by your system.
1624 ERROR_INSTALL_TRANSFORM_FAILURE There was an error applying transforms. Verify that the specified transform paths are valid.
1625 ERROR_INSTALL_PACKAGE_REJECTED This installation is forbidden by system policy. Contact your system administrator.
1626 ERROR_FUNCTION_NOT_CALLED The function could not be executed.
1627 ERROR_FUNCTION_FAILED The function failed during execution.
1628 ERROR_INVALID_TABLE An invalid or unknown table was specified.
1629 ERROR_DATATYPE_MISMATCH The data supplied is the wrong type.
1630 ERROR_UNSUPPORTED_TYPE Data of this type is not supported.
1631 ERROR_CREATE_FAILED The Windows Installer service failed to start. Contact your support personnel.
1632 ERROR_INSTALL_TEMP_UNWRITABLE The Temp folder is either full or inaccessible. Verify that the Temp folder exists and that you can write to it.
1633 ERROR_INSTALL_PLATFORM_UNSUPPORTED This installation package is not supported on this platform. Contact your application vendor.
1634 ERROR_INSTALL_NOTUSED Component is not used on this machine.
1635 ERROR_PATCH_PACKAGE_OPEN_FAILED This patch package could not be opened. Verify that the patch package exists and is accessible, or contact the application vendor to verify that this is a valid Windows Installer patch package.
1636 ERROR_PATCH_PACKAGE_INVALID This patch package could not be opened. Contact the application vendor to verify that this is a valid Windows Installer patch package.
1637 ERROR_PATCH_PACKAGE_UNSUPPORTED This patch package cannot be processed by the Windows Installer service. You must install a Windows service pack that contains a newer version of the Windows Installer service.
1638 ERROR_PRODUCT_VERSION Another version of this product is already installed. Installation of this version cannot continue. To configure or remove the existing version of this product, use Add/Remove Programs in Control Panel.
1639 ERROR_INVALID_COMMAND_LINE Invalid command line argument. Consult the Windows Installer SDK for detailed command-line help.
1640 ERROR_INSTALL_REMOTE_DISALLOWED The current user is not permitted to perform installations from a client session of a server running the Terminal Server role service.
1641 ERROR_SUCCESS_REBOOT_INITIATED The installer has initiated a restart. This message is indicative of a success.
1642 ERROR_PATCH_TARGET_NOT_FOUND The installer cannot install the upgrade patch because the program being upgraded may be missing or the upgrade patch updates a different version of the program. Verify that the program to be upgraded exists on your computer and that you have the correct upgrade patch.
1643 ERROR_PATCH_PACKAGE_REJECTED The patch package is not permitted by system policy.
1644 ERROR_INSTALL_TRANSFORM_REJECTED One or more customizations are not permitted by system policy.
1645 ERROR_INSTALL_REMOTE_PROHIBITED Windows Installer does not permit installation from a Remote Desktop Connection.
1646 ERROR_PATCH_REMOVAL_UNSUPPORTED The patch package is not a removable patch package. Available beginning with Windows Installer version 3.0.
1647 ERROR_UNKNOWN_PATCH The patch is not applied to this product. Available beginning with Windows Installer version 3.0.
1648 ERROR_PATCH_NO_SEQUENCE No valid sequence could be found for the set of patches. Available beginning with Windows Installer version 3.0.
1649 ERROR_PATCH_REMOVAL_DISALLOWED Patch removal was disallowed by policy. Available beginning with Windows Installer version 3.0.
1650 ERROR_INVALID_PATCH_XML The XML patch data is invalid. Available beginning with Windows Installer version 3.0.
1651 ERROR_PATCH_MANAGED_ADVERTISED_PRODUCT Administrative user failed to apply patch for a per-user managed or a per-machine application that is in advertise state. Available beginning with Windows Installer version 3.0.
1652 ERROR_INSTALL_SERVICE_SAFEBOOT Windows Installer is not accessible when the computer is in Safe Mode. Exit Safe Mode and try again or try using System Restore to return your computer to a previous state. Available beginning with Windows Installer version 4.0.
1653 ERROR_ROLLBACK_DISABLED Could not perform a multiple-package transaction because rollback has been disabled. Multiple-Package Installations cannot run if rollback is disabled. Available beginning with Windows Installer version 4.5.
1654 ERROR_INSTALL_REJECTED The app that you are trying to run is not supported on this version of Windows. A Windows Installer package, patch, or transform that has not been signed by Microsoft cannot be installed on an ARM computer.
3010 ERROR_SUCCESS_REBOOT_REQUIRED A restart is required to complete the install. This message is indicative of a success. This does not include installs where the ForceReboot action is run.