Weather you should or not depends on the device you have. If you have an iPhone 4 you may want to leave it, many of the transient features of iOS 7 are not available and some will work at a reduced rate. Thinkgs like no parallax or reduced motion between opening apps.
Cached memory is handled differently in iOS7 which will help reduce battery drain,but i found that i means many apps that i would have expected to be available from previous state are not. Its no biggie they just start again.
Privacy and location settings are more easily accessible, a big thing for most people. Along with background app refresh settings, another battery saving feature.
In terms of look and feel, personally i think its great. Getting rid of the faux leather on the calender app when most users in a few years time won't even know what a filofax is, green felt background, fake stitching have all gone. The OS reflects the fact that its on a £500 piece of kit rather than a tesco or argos rip off. These are personal preference.
Also note that you are NOT permitted to submit apps to the app store unless it is designed with the iPhone 5 in mind and iOS7, they can be backwards compatiable but that is optional. So while major developers that can afford to spend the time building backward compatible apps, small companies cannot and you might find they will no longer support or update older apps.