By default when displaying RAW FastRawViewer applies S-shaped tone curve and Adobe compatible' midtone correction.
With these (default) settings, the RAW display becomes more or less "as expected", correlating to the embedded JPEG and standard Adobe rendition (with all sliders in default positions) in both contrast and brightness.
In FastRawViewer 1.7 we've implemented a quick way to turn of both of these settings and switch between a flat, non-contrasty look, which corresponds to what the camera records into the RAW much more accurately, and a regular view.