The main features of the C850 are its 3x zoom Pentax lens and its 2.7-inch high-res monitor. The lens has a zoom range equivalent to approximately 35-105mm, which is about average for a camera of this type. It folds flush with the body and only extends about 15mm at full stretch, so it's pretty unobtrusive. As I mentioned earlier, it appears to be the same lens as found on the Pentax Optio E40, which is no bad thing.
The monitor screen is 2.7 inches with a resolution of 230k dots, which is better than average. However it does have a few drawbacks, the main one being its relatively restricted viewing angle, which is no more than 45 degrees in any direction. It isn't terribly bright either, which combined with the highly reflective surface makes it very difficult to see in bright sunlight.
Apart from these features the C850 doesn't really offer anything beyond the usual point-and-shoot options found on the majority of compact cameras. It has three metering modes (centre-weighted, spot or multi-zone), auto bracketing and adjustable sharpness, but that's about it. There are some optional colour filter modes, but the menu page for these appears to be broken and only monochrome, sepia and red can be selected. It has face detection, but then so does almost everything these days. It also has the latest must-have feature, smile-detection, which waits until the subject is smiling before taking the picture. It seems to work well enough with well-lit subjects relatively close to the camera, but like most such systems it is easily confused.
The camera has a basic Program auto mode and a range of 15 other scene modes covering all the usual situations. There is a mode called "Shake-Free", but this just boosts the ISO setting to its maximum of 1600, with all the image noise problems this usually entails, so it's best avoided.