I don't own Samsung NX100, but I had a chance to use it for 2 months.
Things I don't like about it:
- Its image quality in RAW is not really better than that of m4/3 cameras.
- JPEG quality is worse, especially noise reduction.
- Extreme hot pixeling at slow shutter speeds (slower than 15s).
- When shooting RAW, the camera is slow as molasses. Come on Samsung, it's almost 2011, 3-4 seconds to write a RAW file is unacceptable. If you shoot 3 RAWs in quick succession, the camera will lock up for 10-12 seconds to flush its buffer.
- AF speed is slightly better than E-P1 but still worse than Panasonic GF1.
- Clip-on EVF is pretty poor (on par with my Sony DSC-R1 of 2005 vintage) and really annoying: when you awake NX100 from sleep by tapping the shutter button, the camera is back to using the LCD - even if you were using the EVF before it went to sleep.
- Almost no customization options.
- Slippery body plastic makes it rather difficult to hold.
- Poor flash system: no high-speed sync, no wireless control, external flash (I used SEF-20A) in TTL mode often leads to overexposure.
Things I like about it:
- Lovely screen, really as good as anything.
- Good controls.
- Color response differs slightly from anything else... Samsung sensor used in NX10/NX100 produces great colors, especially I like its tremendously deep rendition of blue and violet tones.
- Cheap lenses. 30mm pancake is half the price of Panasonic 20mm. And for the Ukrainian price of Panasonic 14mm prime I can buy both Samsung NX100 body and Samsung 20mm pancake. (But this is probably not true for the rest of the world.)