The S550's overall performance is a bit disappointing. It takes just under three seconds to start up and around two and a half to shut down again, which is rather slow by premium compact standards. In single-shot mode the shot-to-shot cycle time is approximately three seconds with the vibration reduction turned on, and approximately two seconds with it turned off. The delay appears to be in writing to the memory card, however reducing the image quality to normal rather than fine did nothing to improve this. In continuous shooting mode it can manage one shot a second for the first ten frames, but then slows down considerably.
The autofocus system appears to be the same one as the S600. It is reasonably quick in good light, but slows down noticeably in lower light conditions, and sometimes fails to focus even in light you can read by. However it is a lot less hesitant at longer zoom settings than some previous Nikon compact camera AF systems, and it will focus darkness at close range thanks to a good AF assist lamp.
When I saw the size of the tiny 680mAh Li-ion battery that powers the S550 I was concerned that it would have a very poor duration. Nikon claims a duration of 200 shots, but in fact I was able to shoot well over 200 photos, many of them with flash, over the course of a week before the battery indicator dropped to one bar.
The flash is a bit weak and noticeably darker in the corners of the frame, but it has very good exposure metering even at very close range, and charges quickly enough to keep up in most social situations.
The S550's final image quality has its ups and downs. Exposure metering is very good, striking a nice balance between shadow and highlight detail. Unlike some other recent compacts the S550 has no facility to boost dynamic range, but nevertheless it coped well with high-contrast situations. Colour rendition is very good, with rich natural tones and plenty of detail in highly saturated areas. One weak point however is the lens, which is rather soft right across the frame and especially in the corners, which rather lets down the potential quality of the sensor. It also produces a lot of uneven distortion at the wide-angle end, and the Distortion Control feature doesn't help much.
Image noise is also a bit of a problem, with some colour mottling even at the minimum ISO setting, and significant loss of detail at 400 ISO. As is usually the case the very highest ISO settings - 1600 and 2000 - produce very poor results, with major loss of detail and distorted colour balance.
The CoolPix S550 is a likeable little camera, very simple to operate and producing good results in most normal situations. It is solidly made and sensibly designed, and has very good handling despite its small size. The 5x zoom range gives it greater versatility than typical pocket compacts, and the electronic vibration reduction helps to cope with the longer telephoto end. Overall performance is a bit slow by current standards, and final picture quality has a few problems, but on the whole it acquits itself reasonably well. The only question is how will it measures up to its recent competitors.