Went on a tour of the La Fenice opera house and ended up buying tickets for the royal box to watch the Opera the next evening. It was a great albeit expensive experience but think my wife enjoyed the opera more than I did.The Tales of Hoffman is on at La Fenice while you are there.
A concert/opera there is not an event to be missed.
Unfortunately there is nothing on when I am there this time.
Fantastic building though and one I would recommend anybody to visit while in Venice.