IOS 7 was released to all apple products using IOS with a 516MB ram or more. It has a completely different interface to IOS 6 and some people find it annoying and ‘tacky’ after downloading it, thinking it was excellent. People think it was amazing due to Apples advertisements but when they downloaded it they found that it was not compatible with some apps and they had to wait for an update that is compatible with IOS 7.
Another downside with IOS 7 is that it is not compatible with an Apple device that has a ram lower than 516MB so you can not download onto the iPod touch 4th gen and lower and not on the iphone 3rd gen or lower.
Overall IOS 7 does have some ups but not enough of them to equal the loss of popularity due to the downs and now you can not downgrade back to IOS 6 as that was stopped by Apple merely a day ago. I would say that if you already have it, it doesn`t matter but if you are still using IOS 6 on a device compatible with IOS 7, keep IOS 6.