We stayed at La Sacca for three nights as part of a trip around the lakes. The room was good, nice size and everything was clean and tidy. If I was to be picky I would say the bathroom was a bit dated - coloured suite, cramped and a fairly small shower.
We had an enclosed balcony with a good view of the lake, which was ideal as it kept out the plentiful mosquito's.
Breakfast was amazing - loads of choice and set in a lovely big dining room with a lake view.
My concerns with La Sacca are that we had anticipated it had a restaurant as part of the facilities. However, this was not the case. This links to the wider issue of location. The hotel is set on a main road about a mile from the centre of Stresa. I would suggest you would have to be very brave to walk it - on the initial section there are no pavements and cars are not driving slowly! This meant that we had to drive into Stresa to eat and try and find parking - which proved nearly impossible in high season.
On the basis of location and lack of restaurant I would not return to the hotel, but if this is not an issue for you then it is a nice place to stay with friendly and helpful staff.