We stayed here for 2 nights in early August 2019 and loved our stay!! We splurged for one of the rooftop jacuzzi terraces and were glad we did -- what a great way to enjoy the glorious views in this city! The check-in experience was easy and professional, and we appreciated Sabin's assistance with getting our luggage to the room and orienting us. The room itself felt very luxurious, and we liked that there was a complimentary welcome bottle of wine present on our arrival. Also appreciate that small things like yogurt, cereal, and milk were available in the room for no charge, and the fridge was stocked with beer and wine at very fair prices (nothing like what you're charged for these things in the USA!). There were also robes in the room for us, which we liked, but one of them -- as well as a pool towel -- was in fairly old condition and ripped in a few places (however, we didn't bring this to anyone's attention but am sure that if we did, it wouldn't have been a problem to get them replaced).
The only real issue we had was with breakfast -- we were instructed to let reception know when we'd like it delivered to our room for the following day, which we did each day. We'd asked for 0900 on Saturday, but when it hadn't arrived by 0930, we called and were told it would be there soon (no apology or acknowledgement of the delay). We had a 1200 flight on Sunday and thus requested breakfast at 0800; it was about 30 min late and only came after we called, and again, no apology. There's a Nespresso machine in the room and the breakfast itself was fairly simple, but still always nice to have fresh fruit and bread and fresh-squeezed OJ, so can't complain beyond that :)
In the common/living room, there is also a full bar available for guests to help themselves to on an honor-system basis, which was a nice touch. The shared outdoor area is perfect, too, with a few nice tables and chairs both in the sun and shade, and we really loved the pool.
The location is also fabulous -- felt very central for us and we were able to walk to most places in the city over the two days we were there. Casa Balthazar seems to be surrounded by lots of yummy authentic Portuguese restaurants -- seriously any direction we walked, the options were plentiful -- and we appreciated one of the host's recommendations to try Oficina do duque for one of our dinners, which didn't disappoint and was really high-quality especially considering the price. Not sure how authentic/local/non-touristy they were, but plenty of Fado places in the area, too.
So overall, we loved our stay and will definitely come back here next time we're in Lisbon! Highly recommend!