What is the Unified Renderer (option on the render tab ithink), the rendering seems to take longer.
Is it a better renderer?
J.
Ugh…
I think this question is answered once a month 
I’m sure you would have got the answer by checking the forum (for example https://blenderartists.org/forum/viewtopic.php?t=4662&highlight=unified+render
)
In any case:
Blender standard renderer renders in passes. First all standard materials, then materials with alpha, then halos and flares.
This, expecailly for halos and flares, can cause some bad overlapping. I was also told by an High Guru that colors are less bright.
THe Unified renderer does this all in just one pass, and things usually looks better.
Stefano