(from "About" article below. Security fixes listed in separate doc.)
"The OS X El Capitan v10.11.5 Update improves the stability, compatibility, and security of your Mac, and is recommended for all users.
This update includes the following enterprise changes:

Fixes an issue where applying a configuration profile to set allowSpotlightInternetResults to False would cause Spotlight to use large amounts of CPU time.

Fixes an issue where applying a configuration profile to set ShutDownDisabledWhileLoggedIn to True would have no effect.

Fixes an issue where only a single NetBoot image would appear in the Startup Disk pane of System Preferences, even if multiple NetBoot images were configured on the server."

Download of OS X 10.11.5 Delta and Combo updaters:

• Download OS X El Capitan 10.11.5 Update (759.1 MB)
  
  
• Download OS X El Capitan 10.11.5 Combo Update (1.53 GB)
  
  Related Apple Support Articles:
• About the OS X El Capitan v10.11.5 Update
  
  
• About the security content of OS X v10.11.5 and Security Update 2016-003

Downloads of Security Update 2016-003 for OS X Mavericks and Yosemite:

• Download Security Update 2016-003 Mavericks (370.9 MB)
  
  
• Download Security Update 2016-003 Yosemite (454.8 MB)

Nvidia Driver Updates: See May 17th/18th news page for Nvidia driver and CUDA updates for OS X 10.11.5 and the new build numbers of OS X 10.10.5/10.9.5 with Security Update 2016-003 installed.

With another multi-OS update release, update servers may be swamped for awhile. For OS X I'd use D/L updaters (combo is an old tip). You can also check the Apple forums for early feedback/problems. (Granted that's like Apple's ER, but with only volunteer help.)
 

"Now enjoy all of your music, movies, TV shows, podcasts, and more in a simpler design.

Navigation. Now you can use Back and Forward buttons as you navigate between your Library, Apple Music, iTunes Store, and more.

Media Picker. Easily switch between Music, Movies, TV shows, and more - and Edit to choose just the items you want.

Library and Playlists. Use Sidebar to view your Library in new ways. Drag and drop songs to easily add them to Playlists. And Edit Sidebar to show only your favorite views.

Menus. Menus in iTunes are now simpler and easier to use. Use the View menu to customize your Library or try context menus to act on specific items."

(The windows version of iTunes 12.4 includes an installer related security fix.)
 

• OS X GarageBand v10.1.2 (OS X 10.10 or later)
  - Stability improvements and bug fixes
  - Contains multiple enhancements to Accessibility
  
  
• iOS GarageBand v2.1.1 (iOS 9.3 or later)
  - Quickly navigate long lists of Apple Loops using a new alphabetical sidebar
  - Use Multi-Touch to select multiple regions simultaneously in the Tracks area
  - Send songs as an audio file using AirDrop
  - Share GarageBand songs via Mail as uncompressed audio
  - Apply your own custom images to songs shared to YouTube and Facebook
  - Support for Shared iPad in iOS 9.3
  
  
• OS X Server v5.1.5 (changes from app store page)
  Profile Manager
  - Configure grace period before passcode is required on Shared iPad
  - Support for skipping the True Tone Setup Assistant pane introduced in iOS 9.3
  - New Restrictions (supervised only): Allow Diagnostic Submission Modification
  - New commands (Shared iPad only): Enable/Disable Diagnostic Submission and App Analytics
  
  
• About the security content of Safari 9.1.1 for OS X 10.9.5 and later
  (included in OS X 10.11.5. OS X 10.9.5/10.10.5 via software update.)
  
  
• iOS 9.3.2 Release notes
  (Some reports of bricked iPad Pro 9.7" (error 56) after the update.)
• About the security content of iOS 9.3.2
  
  
• Apple TV (4th gen) Software Update 9.2.1 simply says
  "includes general performance and stability improvements."
• About the security content of tvOS 9.2.1
  
  
• watchOS 2.2.1 Information (release notes)
• About the security content of watchOS 2.2.1