I particularly found its high-end frequencies harsher than the Yamahas, especially when adding the upper register, and it sits worse in the mix when compared to it (to my ears). I found myself playing in the same place, the same songs, with a Nord in some occasions, and the CK in others. Clearly, the sound operators cut more frequencies when I use the Nord and in the end, I hear less of it in the final result and the sound is less pleasant. It is the other way round, however, when it comes to the Rhodes.
It's the Hammond style 'click' - the percussive element of the keys. I can't speak to the CK's sounds, but in many keyboards that is an option element of the organ sound.
