It is unknown.
All that is known so for sure so far is the Forerunners are creators of the technology behind the Halo rings and that humans can activate the technology. As to what their society was like, that is speculation unless Bungie/MS create more Halo games that delve into the Foreunner's background.
It is most likely that they are good, as they were never at war with one another, and they sacrificed their own race for the sake of all the rest.
never describe a species as good or bad they had somme mistakes and somme triumphes.