I’m not sure if this is in the correct place, but here it goes:
Blender’s particles are in bad condition. Not as bad as they could be, but I know the Blender developers are much better than that (the fact that we have Blender today is a testament to Blender’s developers, as Blender used to be a mess in a CVS repository).
First of all, particle deflection is in bad shape. Particles ignore the deflecting object (if someone can help me out here, that would be great), passing straight through it.
Secondly, and this one is a little more complex/fanciful. Particles should probably be volumetric. This would help clouds, smoke, fog, etc. effects look much more realistic.
Also, some raytracer changes are desired. My main annoyance right now is the lack of ray depth above 10. Although it is a good way to keeps new users saze, I would recommend simply complaining loudly at high ray depth values, and asking “Are you sure? (High values could freeze your computer)” at least twice, but I feel that many of my scenes would look better with more ray depth. If someone could please help me find workarounds, or better yet fix these problems I would be much easier off