We absolutely loved Palazzo Gradenigo and will definitely stay there again. It is a magical place and set the mood for our entire stay in Venice. It was an unforgettable experience and we feel very fortunate and privileged to have been able to stay there.
The apartment is enormous and has breathtaking views of the entire Rio Marin canal. The location is perfect. A few minute walk to the train station, 1 minute from the grocery store and a 20 minute walk to Piazza San Marco. The walk to anywhere is gorgeous. We only ran into big crowds near Rialto Bridge and San Marco. Otherwise, around Gradenigo, it's much better - not empty but definitely not over-crowded. A walk at night is beautiful.
The only negatives are the heat and mosquitos. Even with the windows closed, we would get startled awake by the high-pitched buzzing in our ears until we learned to cover our ears with blankets. We didn't have repellant so we all got lots of itchy red bites. The heat wasn't unbearable but the apartment wasn't much cooler than outside which was around 80-85F. The apartment comes with 4 fans which we took advantage of.
The building is architecturally gorgeous. From the windows, we saw many tourists snapping pictures of it and the canal. Also from the window, you can see a gondola station. We used them and it was great - our gondolier was very friendly, gave us lots of history and info and spoke of the sights.