The first thing that strikes you about iOS 7 is that it is not, in some ways, very "Apple". It has a new, clean look, with flatter and simpler icons than previous. Some have even gone so far as to say that it has "borrowed" this approach from Microsoft's Windows Phone. It also has some additions in terms of the new notification centre and methods of swiping that seem to be "borrowed" from Android, too. For some it is surprising that Apple seems to be deriving elements from elsewhere, but it also indicates a general convergence that is going on with operating systems.
Battery life seems worse than before. Previously I was getting about 9 hours typical usage on the test machine, an iPad 2. This is now down to about 7. Some of this is due to background processes running all the time, and these should be switched off unless particularly needed. For instance, if you look at the screen background and move the iPad/iPhone slightly you will see that it moves, creating a sort of parallax or 3-D effect. This can be switched off to improve battery life.
Everything seems slower, too. Not so much that it drives you mad, but it is noticeable in some areas. On a slower device, such as an iPhone 4, this possibly has more of an impact.
Probably the worst thing about iOS 7 is the new version of Safari. It crashes regularly on my iPad. It is slower than its predecessor. The address bar and search box have been combined into a single thing, as is the fashion these days, but it just doesn't seem to be as well done as elsewhere. Changing the options - and some of the options simply don't work - is still not done in Safari itself but rather in Settings. Accordingly, I've switched to Chrome, which behaves far more conventionally and addresses these areas. You can't actually remove Safari or do without it entirely, but for everyday use Chrome is currently a lot better.
It is true that the above comments focus mainly on the negative aspects of iOS 7. It can be expected that Apple will quickly roll out fixes for any deficiencies. In the meantime, if you haven't switched to iOS 7 yet then you might want to put things on hold for a little while.
Overall impression? Why, 7 out of 10 of course.