The quality of the particles depends on the quality and the type of media you use and how you choose to use the particle generator knowing its limitations.
As with any particle generator of pixel based media when you scale an image to anything beyond its original display size you will end up seeing pixel scaling artifacts.
The options are to either create a much larger image in pixel size, say 1000 x 1000 pixels instead of just say 400 x 400 pixels. Try larger for better results.
The other option is to apply the blur pixel fx to the layer slightly.
Just as a
sample...
This is a loop created at 640x480 res loaded into modul8 and you can see that as I scale up the particle size, the particles generated that are close to the 'camera' lose quality. Later on in the clip the situation gets worse and then improves again when I mess around with the 'alpha' 'in' and 'out' properties.
There is really a lot to play with here. I am always finding new ways to have good quality fun with this tool way beyond just flicking it on.