We sailed last June on the Star in cabin C319 and the balcony was big. The people above can see down onto half of your balcony but the rest is covered and private.
We spent lots of time on the balcony in port watching sea planes, eagles and people and it is a must for scenic cruising. I can't imagine going to Alaska without having a balcony.
The Star was a great ship and we did not have one little thing wrong, it was a wonderful trip.