Mine is running okay, but battery is horrible. My battery was already pretty bad with iOS 7 and the update just made it worse. I don't feel like shelling out money for a new battery since I'm close to my upgrade anyway. I get maybe 4 hours of usage if I'm lucky.
Switching between keyboards (I have three, English, Emoji, and Korean) is kind of laggy and doesn't always register so I have to hit the globe key several times. Third party keyboards are also especially laggy for me, but that's probably an app issue and not the phone or iOS.