Funny you should ask this: I was a bit put out the other night to be seated in the far left mezz for The Piano Lesson, behind the box, so that the title instrument couldn't be seen (until it's moved out farther late in the play). I missed not seeing the carvings described in the play. Otherwise 3d row front mezz was a fine seat.
My experience as a long-time member is that my seats have been very good maybe 85% to 90% of the time off-Broadway, 70-75% on Broadway. I've sat anywhere from the first row to the very last row of the mezzanine...It's been a long time since I was in the balcony.