The most important parameter for Denoise3d is TIME.
The default setting of 6.00 is just too high and causes smearing.
Setting time to 4.00 seems to be a good compromise and causes no visible problems for me.
The default settings for Luma (4.0) and Chroma (3.0) work well for me.
The above settings do soften the image slightly but I compensate for this by using a bit more Descaler sharpen.
I have experimented with a combination of Denoise3d and Gradual denoise as per llamameat's suggestion, but I just could not come up with a combination that improved on Denoise3d used alone before any resize.
I never liked Gradual denoise used before resize due to the visual artifacts it created. This is one of the reasons I started using resize in the first place. It allowed filters to be used on an up scaled image for a more subtle effect.
Denoise3d may work better after resize as well but even today's fastest PC's can't cope with that.
Anyway, I find that Denoise3d works very well before resize. And is the best noise filter I have ever used. Including the filters for Virtual Dub and AVISynth. And before anyone asks, I have not used Virtual Dub or AVISynth fiters in ffdshow.
The ffdshow resize-sharpen dude.