I gotta admit that there are days when this phone is the worst.
There are times that it is so laggy (20 seconds to open an app) that I have to restart it. Also, the phone app is ALWAYS laggy.
I constantly close the "running" apps and I use the Fast Reboot app as well.
Battery life: Some days it lasts all day, other days it might not make it through lunch. When I look at the battery usage, apps that I haven't used in days or weeks are sucking huge amounts.
It's a good phone, but there are days when I regret getting rid of my s4.