Passive will be less bright than active due to the technology when compared to another set with the same illumination.
As noted earlier resolution is also reduced. I'm not convinced its a good trade off at this point.
I don't at all disagree that some of the attributes of passive 3d like cheap glasses and reduced flicker are attractive.
Passive will have a place when we get UHD passive 3D LCD panels that will allow full 1080p resolution. Until then people will be watching 3D blueray content with significantly reduced resolution.