The BoS aren't good or bad per say. They are isolationist and xenophobic for the most part, with the DC chapter being a notable exception. Depending on when we see them they tend to sway slightly from the grey on the moral spectrum, one way or the other.
The initial brotherhood were a secretive group that made damn well sure anyone not from the brotherhood kept their distance. They would take technology from the wastes, presumably flexing their technological advantage on anyone who protested, and horde them away... even non-military tech that could benefit the wastes. As a result of the Super Mutant horde, they also develop a huge case of xenophobia towards mutants of all kinds, which becomes apparent in later eras.
In 2 the Californian chapters are getting battered by the Enclave who are technologically superior and 1000% more crazy. This version of the Brotherhood is still secretive and isolationist, but they know they need outside help to beat the enclave. The Enclave possessed the same hubris of the brotherhood, therefore didn't see wastelanders as a threat, which the Brotherhood tried to use to their advantage (assisting some smelly tribal to do their dirty work).
In 3 we see a side of the Brotherhood that is hinted at but often suppressed. This chapter is far more altruistic and are willing to put themselves on the line to help the wasteland. But it's a contentious stance and a splinter group travel the wastes doing what brotherhood do best but with an even greater helping of scorn and nasal gazing, making for an uneasy tension between the 2 groups. Talking to the Mutants in Underworld reveals that even the "good" brotherhood aren't exactly enlightened, as they don't value Ghoul lives very much if at all.
New Vegas shows the end times of the old brotherhood ways and either their demise or reform. Isolating themselves made them weak, rejecting new blood made them few and their tech no longer yields an advantage as the collapse of other chapters as well as the enclave has resulted in a lot of tech becoming more widely available, if still uncommon, out in the wastes.
Fallout 4 see's the Altruistic reformed brotherhood take a few too many cues from their old Enclave nemesis. They are now a force that operates in the open and in large scale deployments. They even recruit wastelanders to their cause to bolster their numbers. They speak of greater good and at some level they are genuine. But they are totalitarian, bordering tyrannical. On top of that they still hold to old xenophobic tendencies towards mutants, even though there are numerous examples of reformed Super Mutants and entire communities of ghouls that get by peacefully.
The BoS for the most part only had their own interests in mind, yet when they finally opened up to help others it quickly became a warring faction set on conquering the wastes, even if peaceful wastelanders get trampled underfoot. The BOS has potential to be a great force for good, but instead we are seeing a revival of the Enclave, minus old world rhetoric and propaganda.
