Bearing in mind that this is a pre-production model, the image quality from the jpeg files looks impressive. (I haven't yet been able to assess the raw files yet.) The jpegs are a little flat right out of the camera (at the default settings) but they're sharp and well detailed and only need a little Levels adjustment to make them pop. Colours are natural in the Standard mode, and even the Vivid mode seems to stay on the right side of garish. The noise in particular is kept well under control. At ISO 1600 it's barely visible and although the noise is fairly course by the time you top out at ISO12800 the images are still usable. In my ISO comparison with the Panasonic Lumix GH1 that I also had with me the NEX-5 was a good two to three stops better.
To be fair, having a much larger sensor than the micro four thirds system (23.4x15.6mm compared with 17.3x13.0mm) you'd expect the image quality to be better, but how the Sony stacks up against Samsung's NX10, which has the same size sensor, we have yet to find out. Of course the downside of the larger sensor is that, like Samsung's Hybrid system, the lenses will always be a bit bulkier than comparable MFT lenses.
On paper then, when compared with existing rivals the Sony NEX-5 has a lot to recommend it: its size, its high res flexi screen, the simple interface, the host of clever but useful high-tech features, the general build quality (which on the NEX-5 is first class) and, from my initial impressions, the image quality. Best of all the aggressive pricing is significantly below what I was expecting from a Sony product.
Image Samples (from a pre-production NEX-5)
Above: Taken using the 18-55mm zoom. Below: a 100% magnification of the image above
Above: Sweep Panorama mode. Unprocessed jpeg (top) and with Levels adjustment (above)
Above: At the Vivid Setting
Above: B&W Setting
Above: Auto HDR Before (top) and After (above)
Above: Auto HDR in B&W mode (before and after)
Above: The shallow depth of field possible using the 18-55mm (@50mm)
Above: Macro Mode
Above: Portrait Mode Below: 100% detail
Above: hand-held in Twilight Mode
Above: Using the accessory flash in Slow-Sync mode