I have a Samsung S5 and updated to Lollipop 2 nights ago. The Auto Brightness functionality (or whatever it's called now) simply doesn't work. Click the "auto" tick box and the screen stays very dark; when I go into bright light it doesn't change so it's impossible to see my phone at all in the daylight unless I uncheck "auto" and then manually adjust the brightness. This new OS sucks. I called Samsung and they blamed Google, who wrote and released Lollipop. I called Google and they blamed Samsung stating Samsung screwed up the OS by adding in their own updates; Basically Google wiped their hands of the bugs in the OS. The rep at Google stated the only thing I can do (yes, I already hard-rebooted) is to wait until another OS update comes out. Real nice, Samsung and Google. Screw the customer and refuse to resolve the issue.
Regarding MontanaXVI's note, my power saving mode doesn't have any setting at all, it's either on or off, but no option to change anything. Anyone else have any solutions I can try?