Citadel Spices is the carefully blended concoction that I have created to give Citadel its look. It sharpens, and it adds detail, contrast, vibrancy, and a few other enhancements. If your images are looking bland and need some flavor, consider sprinkling in some Citadel Spices.
It works better with non-realistic models, but it can still work for realism (just start low and work your way up).