I spent a couple of days at Copacabana Mar Hotel, i found it very clean, with staff who are always available, very friendly, and ready to help and provide information.
The location is perfect, allowing you to reach the beach or the metro in just a few minutes.
As for the building, it is quite dated and would benefit from substantial renovation and modernization. The rooms are not particularly quiet, and the beds are not the most comfortable.
The breakfast is good but could be improved with a wider selection of fruit and pastries.