If you were wondering about the view from the absolute back row in the nose bleeds section of the auditorium (I'm talking about the last floor of the opera house) I can tell you that you'll have no problem seeing everything on stage and hearing everything crystal clear, also they have subtitles in French and Dutch up there as well.
HOWEVER if you are above 175 cm in length I would strongly advice against buying a seat in any of the rows in this part of the opera. It is extremely cramped up there leg room wise, and I do mean extremely. My knees were almost covering the line of sight of the woman sitting in front/underneath of me, that's how bad it is, But then again, if you manage to book a seat at the very beginning or very end of the row, you'll be able to sit quite comfortably, So I say again, don't try one of these seats if you're above 1,75 in height or if you are over-weight, have knee issues or poor blood circulation in your legs.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.