gHacks uploaded a nice summary of the 34 updates:
Most of these updates fix small or rare issues and as such they aren't mandatory but they can be useful if you're experiencing issues. You can download these patches via Windows Update.Update for Windows Server 2012 R2 (KB2998097) - "Specified account does not exist" error message when domain users try to change their password in UPN format in a different domain
Update for Windows 8, Windows RT, and Windows Server 2012 (KB3003729)
Update for Windows 8.1, Windows RT 8.1, Windows Server 2012 R2, Windows 8, Windows RT, Windows Server 2012, Windows 7, and Windows Server 2008 R2 (KB3013531) - Update to support copying .mkv files to Windows Phone from a computer that is running Windows
Update for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2 (KB3013538) - Automatic brightness option is disabled unexpectedly after you switch between PC settings pages in Windows
Update for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2 (KB3015696) - The InputPersonalization.exe process crashes in Windows
Update for Windows 7 and Windows Server 2008 R2 (KB3020369)
Update for Windows 8.1, Windows RT 8.1, Windows 8, Windows RT, Windows 7, and Windows Server 2008 R2 (KB3020370) - Update the copy of the Cmitrust.dll file in Windows
Update for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2 (KB3021910)
Update for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2 (KB3022345)
Update for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2 (KB3033446) - Wi-Fi connectivity issues or poor performance on CHT platform computers in Windows 8.1
Dynamic Update for Windows 8.1 and Windows Server 2012 R2 (KB3036216) - Compatibility update for Windows 8.1 and Windows Server 2012 R2: April 2015
Update for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2 (KB3037924) - You cannot do System Image Backup to Blu-ray media in Windows
Update for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2 (KB3038002) -UHS-3 cards cannot be detected in Windows on Surface devices
Update for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2 (KB3038562) - Cannot access DPAPI data after an administrator resets your password on a Windows Server 2012 R2-based domain controller
Update for Windows 8.1, Windows RT 8.1, Windows Server 2012 R2, Windows 8, Windows RT, and Windows Server 2012 (KB3038701) - Custom Media Size entries are missing in the Print Capabilities document for version 4.0 printer drivers
Update for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2 (KB3042216)
Update for Windows 8.1, Windows RT 8.1, Windows Server 2012 R2, Windows 8, Windows RT, and Windows Server 2012 (KB3043812) - Layout of Cambria font is different in Word documents when the text metric changes in Windows 8.1 or Windows 8
Update for Windows 8.1, Windows RT 8.1, Windows Server 2012 R2, Windows 8, Windows RT, and Windows Server 2012 (KB3044673) - Photos taken by certain Android devices show blank value in Date taken field in Windows Explorer
Update for Windows 8.1, Windows RT 8.1, Windows Server 2012 R2, Windows 8, Windows RT, Windows Server 2012, Windows 7, and Windows Server 2008 R2 (KB3045645)
Update for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2 (KB3045717) - Narrator does not stop reading when you press Ctrl key in Windows
Update for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2 (KB3045719) - Microsoft Project Siena crashes when you use galleries in the application in Windows
Update for Windows 8.1, Windows RT 8.1, Windows Server 2012 R2, Windows 8, Windows RT, and Windows Server 2012 (KB3045992) - "Description cannot be found" error in event logs in Event Viewer in Windows Server 2012 R2 or Windows Server 2012
Update for Windows 8.1 and Windows 7 (KB3046480) - Microsoft Project Siena crashes when you use galleries in the application in Windows
Update for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2 (KB3046737)
Update for Windows RT 8.1 (KB3046743) - Update to reduce Office servicing footprint in Windows RT 8.1
Update for Windows 8.1 and Windows RT 8.1 (KB3047254) - Stop error 0x0000009F when you use the Bluetooth Hands-Free Audio and Call Control HID Enumerator driver in Windows 8.1
Update for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2 (KB3047255) - "0x0000009F" Stop error when a Windows-based computer has two USB devices connected
Update for Windows 8.1, Windows RT 8.1, Windows 8, and Windows RT (KB3047276) - Update APN database entry for Cubic Mobile (Liechtenstein) and Verizon Wireless (US) in Windows 8.1
Update for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2 (KB3047641) - Secure Channel improvement for Windows 8.1, Windows RT 8.1, or Windows Server 2012 R2
Update for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2 (KB3048043)
Update for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2 (KB3048097)
Dynamic Update for Windows 8.1 and Windows Server 2012 R2 (KB3048100)
- Compatibility update for the web, store, and media upgrade experience is available for Windows 8.1 and Windows Server 2012 R2: April 2015
Update for Windows 7 and Windows Server 2008 R2 (KB3048761) - Information or messages are not updated automatically in an application in Windows 7 or Windows Server 2008 R2
Update for Windows 8.1 for x64-based Systems (KB3053946) - "0x00000113" Stop error when you wake a computer from sleep mode in Windows 8.1