The RX100 uses a Zeiss T* coated lens; based on my experience with Sony's camcorders, the T* lenses are significantly better than the uncoated ones. While the lens starts at a wide f1.8 maximum aperture, by the time it hits 100mm it devolves to f4.9, which is pretty narrow, especially compared with cameras like the Fujifilm X10 (f2.8), the next sensor-size down. Sony claims that at least it doesn't drop off precipitously after the first zoom stop or two.
The RX100 incorporates the same sort of control ring that Canon debuted in the S95 and which was then incorporated into the Olympus XZ-1. Like those models, the ring supplies context-sensitive adjustments to various shooting settings, such as shutter speed, aperture and ISO sensitivity. In order for silent operation during movie shooting, Sony's doesn't have any tactile "click" or stops for the ring; I prefer a little more physical feedback.
Sony's popup flash can be tilted back while shooting. The ability to bounce the flash -- or simply reduce the harshness and intensity without having to dive into the settings -- usually results in much better flash photos.