I'm not a fan of iOS 7 design-wise, but my biggest gripe is the battery. It's bad. Really, really bad. I think it's a combination of an actual decrease in battery life and iOS 7's terrible monitoring of it.
It's not uncommon for my phone to shut down after it's hit 8% remaining battery. Or I'll be watching a video with 45% left, and the next second it'll cut me down to 25%. There have been a few instances where I've gone from ~25% to completely empty in a flash, leaving me with a dead phone much earlier than I'd anticipated. So now I really can't leave my place for more than maybe 4/5 hours without my charger.
It's not uncommon for my phone to shut down after it's hit 8% remaining battery. Or I'll be watching a video with 45% left, and the next second it'll cut me down to 25%. There have been a few instances where I've gone from ~25% to completely empty in a flash, leaving me with a dead phone much earlier than I'd anticipated. So now I really can't leave my place for more than maybe 4/5 hours without my charger.