Until the (rather sexy) new Olympus EP-1 hits the streets next month, the Sigmas are the only compact-sized cameras with large sensors. This means that the pixels are much, much bigger than other compact cameras, generally resulting in less digital "noise" in photographs. And a bigger sensor also means it's possible to achieve a much shallower depth of field in an image (making it possible to throw areas out-of-focus, especially when shooting at f2.8 on the DP2).
What's more, they are also the only compacts with Sigma's proprietary Foveon sensor, which is different from usual camera technology, having a separate layer for red, green and blue, rather than a single layer of interspersed RGB pixels. This means that despite their rather low resolution count (approximately 4.5 megapixels) they produce images with a similar level of detail to other 8-12 megapixel cameras.
One of the most controversial aspects of the cameras is the
design. Some people hate the black minimalist black box-like form (the body of the camera is used as a heat sink for the electronics inside). I think it looks like the sort of camera Dieter Rams might have created. And with the dinky optical viewfinder, it really looks the business.
In use, it's fairly slow, a bit like using a mini medium format camera. Which suits a filmhead like myself. It encourages you to slow down, think about what you're doing. Not ideal for party snapshots, but excellent for more considered work.
With the recent firmware update, the autofocus is snappier (it was dreadful before). And taking the camera out and about with me, I'm in photo heaven. And I've made some really gorgeous A2 prints from the files.