Things that frustrate me in the Android ecosystem in 2015: application backup. As someone who switches phones regularly this problem is amplified for me; but it equally impacts someone who only uses backup in case of catastrophic loss of phone.
Here is my issue - Android/Google Cloud will back up system information as well as my "Application + Data" in Lollipop. I can also restore it when importing to a new phone. However "Data" is a bit misleading here - as it only supports application data that is stored within Google Play.
Many of my most important applications are not supported - ie Bitcoin wallet, Google Authenticator, and JuiceSSH; along with other less important apps like Instagram, Swarm whereas I still need to manually set up the app with my login information and preferences.
Right now for backup there are really two 3rd party choices to fix this issue. Helium - which does not back up many apps including all of the ones mentioned above; and Titanium Backup which requires root access (but besides being not very user friendly is an absolutely fantastic app that I wholeheartedly recommend).
So as the ecosystem stands right now; you either root your phone and use Titanium Backup for a real system backup - or you don't root your phone and lack the basic protections regular backups are supposed to protect against.
As data protection is at play here - each app is 'siloed' and can only access certain data on the phone for security reasons; this needs to be an Android core issue and I hope more focus is put into this in the future. Not everyone has access to or wants to back up data to Google Play; Android users need external solutions that are easy enough for 'regular users' who do not need to root their phone to create a full backup.