This lens is priced inline with other consumer lenses with the same specs (Nikon / Canon / Panasonic) - mid-to-long telephoto in the f/4-5.6 range with stabilization, but the build and image quality is exceptional.
Handling on the NX100 is a little different than with a similar lens on other systems - the lens weighs a little more than the body and drastically changes the balance. In practice it works well as you support the bottom of any zoom with your left hand anyway, so shooting is comfortable but different in that all the weight is in that hand since the camera weighs so little. Carrying the camera on the strap with this lens mounted will also leave the lens pointed down, rather than out, but the zoom is tight and there is no barrel creep. (The other system lenses are so small that the body usually lays flat against your torso on the strap.)
I own the Nikon 55-200 f/4-5.6, and have used the canon equivalent in the past. In comparison this lens is more solid with a better feel in your hands. Zooming feels smooth and purposeful, while the Nikon version feels cheaper and more plastic. The Samsung mount is metal (plastic on Nikon), and overall fit and finish are superb.
Images are sharp and vibrant, stabilization is smooth and quiet, while the focus is quick and silent. The Samsung system lacks a direct connection to the focus helicoid, but manual focus feels nearly as direct and the results are just as good. Near-to-far focus is about 1.5 turns, excellent for precision work. Autofocus is quick and quiet, more so on both accounts than the comparison lens.
I expected this lens to be similar to the competing systems in terms of quality and performance, but I have been pleasantly surprised in every way.