I wouldn't say I'm a yuge fan of it, but I do like the idea behind it. It's refreshing, despite being a pretty 'small' change when you think about it. The thing is, when you have a smaller screen it may be a bit more obstructive than when you have an iPhone 6/6s/7 or of course an iPhone 6 Plus/6s Plus/7 Plus. Apple seems to be doing this more often over time. For example, iOS 8 came with some design changes that were really focused on the bigger iPhone 6/6 Plus. It looked like iOS 10 'fixed' this for a part, being a more universal OS in that regard. But with iOS 11, they went back to that idea. Might be overthinking all this, but that's at least my opinion. 
But you know, I do understand it up to some extent. It might not be the last version of iOS available for 4-inch iPhones (there's still the iPhone SE for example), but at some point it WILL be the last version to support those smaller devices. Even so, they should've tweaked the design a little bit to adapt to the size of the phone. More so than it does now at least.
Anyway, I myself like the direction Apple is going. I know people were expecting, or at least hoping for a complete overhaul of the design. But I think the fact that Apple 'phases' design changes into smaller blocks is a much better approach. The new Control Center is a perfect example of that, but also the notifications and widgets design from iOS 10 and onwards show that they do change their design. They do it even in a smart way, making it really complement the devices with 3D Touch (again, Control Center and notifications!). Heck, the way the search bar is now 'integrated' with the title bar looks pretty amazing to me. I hope they continue with this design approach.
Obviously, there are things that I do not like too much about the design, there's no denying about that. But overall, iOS looks really grown up to me from a design perspective, as well as from a functional perspective.
So far my two cents.
But you know, I do understand it up to some extent. It might not be the last version of iOS available for 4-inch iPhones (there's still the iPhone SE for example), but at some point it WILL be the last version to support those smaller devices. Even so, they should've tweaked the design a little bit to adapt to the size of the phone. More so than it does now at least.
Anyway, I myself like the direction Apple is going. I know people were expecting, or at least hoping for a complete overhaul of the design. But I think the fact that Apple 'phases' design changes into smaller blocks is a much better approach. The new Control Center is a perfect example of that, but also the notifications and widgets design from iOS 10 and onwards show that they do change their design. They do it even in a smart way, making it really complement the devices with 3D Touch (again, Control Center and notifications!). Heck, the way the search bar is now 'integrated' with the title bar looks pretty amazing to me. I hope they continue with this design approach.
Obviously, there are things that I do not like too much about the design, there's no denying about that. But overall, iOS looks really grown up to me from a design perspective, as well as from a functional perspective.
So far my two cents.