We spent an extended holiday weekend with our two kids in Buzios and decided for the Serena because of its location, close to the beach (one block away is the beautiful Geribá beach) and also because we like the "boutique hotel"-flair.
The weekend was beautiful and we had a very good time at the hotel, enjoying the nice layout of the hotel grounds and the relaxing atmosphere. The kids loved the pool, although a rather small one, and the kids corner.
Food at the restaurant was good, the Picanha was excellent; the breakfast buffet was very complete. However, the staff could be a bit more attentive (e.g. when we were sitting by the pool, they never offered pro-actively any service; yet if we asked for it, we always got what we wanted)
The rooms are very nice, however the bath-room is minuscule, way too small.
The hotel offers a transfer to the city's restaurant area at night, which is quite convenient.
Wifi is free and available all over the hotel with good quality.
One negative aspect was the smoking: the hotel is Argentinean owned and there is a large presence of Argentineans in the hotel, which actually adds a nice international flair to the hotel. Yet, they seem to care less about not smoking in public areas and the hotel staff did not bother either. Thus, frequently people sitting by the pool or on the terrace of the restaurant were smoking and it was frequent to find cigarette butts in the garden or in the sitting area by the pool, which was not very nice.