In addition to battery issues, many of the complaints I’ve heard about iOS 7 center around WiFi. After upgrading, many people are getting the dreaded “unable to connect” message. There is a solution that’s been passed around on the Apple discussion forums that should work for most people. You’ll need to spend a couple minutes with your phone and router.
Put your phone into Airplane Mode. Then, go into Settings > General > Reset > Reset Network Settings. Then, reboot your router if you have access and take your phone out of Airplane Mode. You’ll be prompted to join your network again, and it should work this time.
You can do this with Airplane Mode turned off, but several people on the forums say they’ve had better luck with Airplane Mode on.