Another some bloke threw dorian into the debate, which is rather irrelevant or confusing... Not sure what he means but he doesn't mean me...

Modal chords, power chords or whatever you wish to call them merely miss the third interval and therefore have a droning quality that allows both major and minor within the same structure. I love playing in DADGAD as it makes picking out a melody between singing or a counterpoint whilst singing both easy and effective. I also (in standard tuning) do something similar with a three string capo.

As another "some bloke" mentions dorian, I would say that the other mode widely used in traditional ballads, mixolydian can be effective when you largely ignore the third interval too, as subdominant fourths sound so good when looking for a nice cadence. Merely flattening one note in a scale can make such a difference to the chords available without odd sounds.