Great apartment! This is about as central as you can be! The apartment is located in Baixa. This is an area known for shopping and is located around many restaurants (although more touristy). You can easily walk to nearby parts of the city (Alfama, Chiado). Given that it is on a central street, there is some noise. However, it was quiet by a reasonable hour (23:00). A noisemaker can easily drown out any sound if needed. I would certainly not let this deter you at all.
The beds were extremely comfortable. The apartment itself was spacious, clean, and had everything needed to make for a great stay. There is an air condition/heat unit. The host communicates well and was extremely accommodating. The price for the apartment is excellent, really making this a great value overall. I hope to return again in the future.