Well I have done the user app + data restore multiple times on my S4, all I can say is that it never failed for me.
Also about widgets, I always used to get them back actually. I mean I use Nova though, and after doing the restoration all the widgets reappear on home screen, but initially they remain blank, I just have to click on them, check allow, and all the data are back. But unfortunately no idea about Sony or their launcher.
Games and all, they will retain their saves and all too. The only things you'll have to redo are the phone settings (locations, WiFi settings, Sync etc), that's all.
And one more thing I will add here, if you are doing a platform upgrade (from JB to KK) then kindly do it fresh. Whoever says what on XDA just don't give a damn, (AndreiLux is the main culprit for that), it's ALWAYS recommended to do a master wipe and then install fresh. If staying on Android for past five years has taught me anything, dirty flashes always give problems, ALWAYS.