I am using the Canon 5D Mark II for 3 years and carrying a bag with lenses through my trips around the world for a top quality photos. A week ago I bought the Samsung NX300 slim and light camera to carry anywhere for street photography with the flipped LCD and was amazed by the quality of the photos with the standard 18-55mm lens - a total cost of $700. I decided to compare the photos quality with the 5D Mark II in various conditions ISO from 100 to 6400 and put it for survey with my friends, they saw the photos with no indication of the camera brand.
About 75% voted for the Samsung NX300 in various conditions, low light, various ISO, day light, color separation, contrast...
Other advantages Samsung NX300 versus Canon 5D Mark II:
Weight - 600gr versus 1600gr with 18-55mm and 24-105mm zoom lens respectively, note - using the Samsung Pancake prime lenses the Samsung weight even less and aperture is 2 or 2.4.
Size - needless to say, overall volume less than half
Very easy to use - touch screen, larger and better Samsung screen, direct access buttons, can do anything either through the touch or the keys/dial.
Price - under 10% of the 5D Mark II price
LCD angle - very important for street photographer, not intimidating, can shoot above a crowd.
Panorama - very nice capability, easy to use
Sport - 10 shoots per second versus 3, but it is limited by the resolution: 7 continuous in RAW, about 20 in Normal JPG. There is also a fast burst mode.
Special night mode with low ISO by taking 5 fast photos and combining for normal intensity.
Remote control with live view on a smart phone using the built-in WiFi, can 'shoot' at birds and other animals by putting the camera inside their premises.
Auto upload of photos to a hosting server for backup (WiFi)
Miniature pop-up flash (5D doesn't not have that you need to carry a bulky flash).
One touch focus anywhere on the frame (LCD)
Full HD video with adaptive focus, 5D focus in video need to be set manually and is very slow.
Manual focus - the NX300 automatically magnifies X5 the focused area when you touch the focus ring, then it immediately reset for the full frame framing.
It is possible to use the Canon lenses with a low cost adaptive ring but need to use manual focus with these.
Can edit the photos on the camera (if you like...) including crop, color, white balance and more
Many other capabilities are similar like AEB bracketing, Preview.
Disadvantages of the NX300
No viewfinder - difficult to monitor the LCD in direct sun light, must put your hand to shade and using the viewfinder is a habit of most photographers that need to get used to a different shooting mode by the screen to get its advantages.
Focus - it is not a real spot like the 5D but rather some small area to focus on
Sometime after power off the camera 'forgets' the previous aperture set-up (probably need to upgrade the firmware soon).