Instagram is a simple and fun application. The simplicity of the application is what led to its success. It is extremely addictive.
However, its most important feature or lack thereof, is the regram functionality. Instagram doesn’t allow users to just repost the same image from another user natively. The absence of this functionality is just wonderful. Users can definitely install third party apps that support this functionality, but, Instagram doesn’t support it natively.
As a user, your feed is usually pretty clean. There’re no non-sensical memes or random images showing up in your feed. You definitely can subscribe to them, but, you don’t see them unless you specifically subscribe to them.
Personally, I think this is great. It keeps the app very focused and clean.