To know a good bounty we should consider the time frame of the bounty, the amount allocated for the bounty, the manager managing the bounty, and the validity of the project doing the bounty campaign.  There are lots of bounties today that offer a reward that is almost non-existent.  They are requiring months of work but the reward is miniscule.  Better learn how to calculate reward base on the participant number if the bounty offer is in stake form.