Summary: I have no idea if this is the fault of the camera (NX300), or the lens. However, I found that when I used it in any of the AF modes, it would not hit focus at the intended point. Without the ability to fine tune these lenses, I found this one to be out of spec IMO. That and the fact that it is only an F2.8 lens make it a 3 - 3.5 star lens to me.
Summary: I agree with the first two reviewers, this is a great quality lens with a very useful focal length. It is approximately equivalent to the kit 18-55 zoom lens when not zoomed. That together with the large sensor and 22MP of my NX200, if I really need to zoom I can just crop the picture in software. Since it is such a pancake, the camera fits into my jacket pocket - much more portable. Like another reviewer said, the 18-55 kit lens is not used much anymore.