"with moving subjects and in limited light the NX1 is the best all-around focus system we've used

"With the 16-50mm S-series lens, the NX1 completely lived up to its billing. It was fast, accurate, and tracked motion very well. Though it wasn't quite as fast with the 85mm f/1.4 portrait lens, we were still generally impressed with the NX1's abilities. It doesn't match up to the Canon 7D Mark II, and there are situations where the Olympus E-M1, Fuji X-T1, and the Sony A6000 are slightly faster, but with moving subjects and in limited light the NX1 is the best all-around focus system we've used in a mirrorless camera."

from http://cameras.reviewed.com/content/samsung-nx1-digital-camera-review?utm_source=usat&utm_medium=referral&utm_campaign=collab

That review also described how difficult it was to edit or even play back the h265 encoded UHD video:

"The only ways we could view what we shot were directly from the camera (which was plagued by artifacting and choppiness) or using Divx 10—VLC, Quicktime, and other common players couldn't play the footage smoothly at all. And even with Divx the only computer we found that could run it was the Razer Blade Pro, a $2,500 high-end gaming laptop. Even our i7-based Macbook Pros struggled. HEVC footage is the future of 4K streaming, but with hardware support at least 18 months away we recommend using a 4K-ready external recorder or converting the footage to H.264 before trying to work with it."

Bill Hollinger wrote:

Also, “it doesn’t match up to the 7D Mark II” really needs some explanation.

You should expect that, though. In terms of on-sensor phase detect points, it's literally covered with them, with Canon's dual-pixel AF turning all the points into AF points. And that's just the secondary system for video and live view. It also has a conventional phase detection array adapted from the Canon 1 DX. Read the 2 pages devoted to AF in the preview of the 7D mark II:

http://www.dpreview.com/previews/canon-eos-7d-mark-ii/6

http://www.dpreview.com/previews/canon-eos-7d-mark-ii/7

If the 7D Mark II didn't have top-ranked AF for a crop-sensor camera, how could they charge more than the NX1 for it, especially when it weighs almost twice as much as an NX1 (even without built-in flash or wifi or an articulated LCD), doesn't do 4K video, doesn't shoot as many frames per second, etc. I don't even know yet if the low-light performance will be better than the NX1; the highly-evolved AF seems like the only reason left to get that kind of camera instead of moving to mirrorless.

J Birn wrote:

the highly-evolved AF seems like the only reason left to get that kind of camera instead of moving to mirrorless.

AF and many more lens options that aren't available yet in most mirrorless systems-- especially at the long end for wildlife or sports photography.

Samsung will keep chipping away at it. The 50-150mm and the 300mm are great new options and I hope many more S lenses will follow now that the NX1 is out.