Unlike its competitors, which use lens-based image-stabilization systems, Sony opts for in-body sensor-shift image stabilization, now dubbed "SteadyShot Inside." One of the A900's distinctive features is the aforementioned Intelligent Preview; hitting the depth-of-field preview button shows a temporary capture of the scene on the LCD, where you can tweak parameters such as exposure, white balance, shutter speed, aperture, and so on, and get a near-live preview of the changes. It's quite a neat idea, but in practice, I found the LCD didn't represent the image accurately enough to make all but the most basic judgments. It also supplies the typical array of features you'd expect to find, including Creative Styles, for customizing contrast, saturation, sharpness, brightness, and Zone (which preserves highlight or shadow detail, depending upon the setting); D-Range Optimizer (DRO) for expanding the dynamic range; and exposure (+/- 3 stops at 1/3 or 2/3 stop increments) white balance, and DRO bracketing. Some pro-oriented features include a compressed Raw format that records 8-bit data instead of the standard 12-bit; (you can read an interesting discussion in Dyxum.com's forum that was raised for the A700 if you're curious); the capability to fine-tune the AF to compensate for back- or front-focus problems (unlike Nikon and Canon's midrange models, the A900 only supports a single setting); and the capability to customize the operation of the buttons and dials. (You can download the PDF version of the manual for more details of its features and operation.)
To support the huge bandwidth required by its large images, Sony supplies the A900 with not one but two of its Bionz image processors. That helps the A900 maintain its respectable close-to-5fps burst rate (though even with a fast UDMA memory card, such as the 4GB SanDisk Extreme Ducati, the buffer fills quickly) and keeps high ISO shots from taking too long to process and save.
A camera in this price range doesn't really need to have great burst performance, but I do expect it to have fast autofocus and single-shot speed. Unfortunately, the A900 doesn't always meet expectations in this respect. For instance, its shot lag under optimal conditions tends to be inconsistent, ranging from as fast as 0.3 second to as high as 0.5 second--the former is quite good, the latter just OK. Shot-to-shot runs about 0.5 second. But my biggest gripe is with the relatively slow autofocus (at least with the 24-70mm f2.8 lens provided by Sony) in dimmer conditions, like indoor lighting. It's slow enough that I missed several shots of active kittens, and tests out at about 1.2 seconds to focus and shoot; that's about the same as a sub-$1,000 dSLR. The Nikon D90 feels more responsive. On the upside, DRO doesn't seem to slow shooting at all.
Technically, I think the A900 produces excellent photos: it has good noise numbers across the range, low color variation, and so on, all of which manifest in the photos. However, after hundreds of photos, I still haven't experienced that "wow" moment I expect from a camera in its class. While it has the capability to produce sharp photos, usually they're not as sharp as I'd like. The high resolution lets you get away with a lack of sharpness, to a certain extent, since you don't have to crop in as far to get the same size print. Photos get noisy and a bit mushy starting at ISO 1,600; I think the Canon 5D Mark II's look better. The color is very good, bright and saturated or subtle when necessary. I have gotten some odd red-to-orange shifts using automatic white balance indoors.
The Alpha DSLR-A900 isn't bad for a first full-frame effort, but Sony has some catching up to do with Nikon and Canon, both of which have had far longer to refine their products in this class. (Though Sony's lack of a huge commitment to optical image stabilization works in its favor here.) I really tried, but I just couldn't feel the love.
(Smaller bars indicate better performance)
(Longer bars indicate better performance)