Casio does make some cameras with very high speed operation, but the EX-Z550 isn't one of them. It starts up and is ready to shoot in a little under three seconds, which is about average for its class. In single-shot program auto mode it has a shot-to-shot time of approximately 2.6 seconds, which is also about average, however in Premium Auto mode the extra processing produces a shot-to-shot time closer to five seconds, which is very slow. Continuous shooting isn't available in Premium Auto mode, but in standard Program Auto mode it has two continuous modes. The standard one shoots at full resolution at 2.2 seconds per frame, while the high speed mode shoots eight frames at 2MP resolution, but at two frames a second.
Casio's autofocus systems have always been very good and the Z550 is no exception. It focuses quickly and accurately in most lighting conditions, and its low light performance is certainly better than average, focusing without a problem indoors at twilight with the lights off. Unfortunately it has no AF assist lamp, so once the light levels drop even further it does have a problem, but it should be able to cope with most social situations.
Image quality is on the whole very good. Exposure is reliably accurate, colour reproduction is excellent and even dynamic range is better than some 14MP compacts, although it does blow out highlights at the slightest provocation. The lens produces very little barrel distortion at wide angle, and while there is some slight blurring and chromatic aberration towards the corners of the frame it's not obtrusive enough to cause a major problem. The main problem with the lens is that it's just not sharp enough. The 14MP sensor catches tons of detail, and the amazingly low compression in Premium Auto mode retains a lot of it, but the lens just isn't sharp enough to match the rest of the hardware.
Image noise is handled a lot better than some previous Casio cameras. Image quality at 200 ISO is smooth and noise-free, and while noise reduction does blur out some fine detail at 400 ISO the overall quality is still very good. Colour gradients and detail lose more quality at 800 and 1600 ISO, and the maximum 3200 ISO is really only useful for very small images, but in this respect the Z550 is no worse than many cameras costing a lot more money.
The Casio Exilim EX-Z550 is a well-made, good looking, easy to use ultra-compact offering a good range of features, a quick and intuitive interface and a reasonable level of performance at a very competitive price. It produces reliable results in most lighting conditions.