Prior to my flight, I went to the Austrian Airlines business lounge in D. The elevator to the lounge was ancient and not easily located. The staff member at the entrance was not welcoming. The food appeared to have not been replenished in some time. The women's bathroom was dated and had an unpleasant odor.
Next, entrance to the flight waiting area was chaotic plus the area had limited seating. Our flight was delayed but no reason was forthcoming. People were encouraged to leave the area to ease the congestion waiting to come into the seated area. They did, but when suddenly the announcement was made that boarding would begin, the masses returned and had issues passing through to the boarding area.
Given those issues, I am still giving two stars because the on-board service was outstanding. Also, the flight was comfortable and arrived almost on-time, despite the delay.
Recommendation: Avoid the business D lounge, if possible. Also, get to the boarding gate early.