Visual Studio 2013, much like its predecessor Visual Studio 2012, also “features” the SHOUTY uppercase menus. Like in Visual Studio 2012, these can be turned off using a registry setting.

tl;dr - run this command in PowerShell:

Set-ItemProperty -Path HKCU:SoftwareMicrosoftVisualStudio12.0General -Name SuppressUppercaseConversion -Type DWord -Value 1