|It's one hell of a... something.|
The SD-1 has a red, green, and blue sub-pixel layered on top of one another. Thus, each pixel in the final image is a full-color pixel. This has a not-undeniable advantage of increased sharpness, since there is no interpolation to blur edges.
That said, the sensor seems to be at a distinct disadvantage in other ways, noise being foremost among them. Oddly, this new version of their sensor has low highlight dynamic range, according to the reviewer, which runs counter to the older sensor found in the DP2 which performed very well in highlight DR and only fell down in the shadow areas.
The single biggest problem with the sensor is that at sensitivities above ISO800, an odd color cast of greens and purples appears over the entire image. This was true of the old DP1 and 2, and it appears that they have been unable to eliminate the issue. Color saturation in general fell off of a cliff after ISO800, and that appears to be found equally on this larger sensor. Basically, color is more important than sharpness. That means that anything above ISO800 is useless.
This is very unfortunate. I wanted to like this camera. There are so many things about its concept that is appealing. Firstly, the file sizes are smaller for this camera than others. For someone who takes lots of pictures, file sizes are a major concern. It requires buckets of computing power to process the RAW files, and they start stretching into the gigabytes after a very short time.
With every pixel being made to display at maximum sharpness, photos are smaller and of superb quality. While I very much want a Sony NEX-7, the 24MP RAW files are not things to which I look forward. And if the Comparometer at Imaging Resource is any indication, the level of detail captured by 24MP appears to be identical to the amount captured by the Sigma. Granted, the RAW files from the Sigma can get pretty big, but the JPEGs never exceed 10MB.
Secondly, it's different! There are so few cameras out there that are truly different. The vast majority of them are using the same concepts, the same technologies, the same layouts, the same everything. This camera dares to be different. That's a great thing and is does present a certain value proposition.
That said, Sigma is balls-to-the-wall insane to charge as much as they are for this camera. I will make a bet with Sigma. I will give them $100 if they sell more than double-digits in any given market. I would honestly be surprised if they sold more than one hundred of these cameras in the entire world. Eight thousand dollars nears the Pentax 645D and it outperforms this camera in every conceivable way. No sane working or enthusiast photographer would ever buy this camera.
And as an aside, the review of the SD1 at Photography Blog almost destroys my confidence in the website entirely. This camera is a disaster. It does not meet its competitors in features, in performance, or in lens selection, yet they still give it four stars. Importantly, all of their test photographs seem to be designed to present as best an impression of this camera as possible.
There are no sample photos above ISO800, they don't mention the saturation issue, and the only images to exceed ISO800 are the "test" images, which are helpfully in almost entirely black & white, thus hiding the horrible saturation problem. Even here, though, one can see the blacks being clipped into oblivion and the total loss of color in the golden metal arms of the pocket watch.
They try their best to compare this to the "disappointing" ISO performance of the Nikon D3X, which exceeds comedy and enters a flat-out lie. The D3X is the number-4 camera of all time at DxOMark's website as regards ISO performance. They extol the virtues of the camera's weather-sealing, then try to rationalize the camera by calling it a "studio camera." Why would a studio camera need weather sealing? They also willfully ignore that the new Sony NEX-7 costs one-eighth as much but captures similar levels of detail, or that the Pentax 645D achieves significantly higher detail and is a true studio camera. This mealy-mouthed review conjures up every point it can in defense of the camera and actively hides points against it. It is a terrible review.