We had a great four day stay at Marta's place. Even though our flight was delayed and we didn't arrive until almost 3AM, both the driver she arranged and the check in hostess were waiting for us.
The apartment is a typical European downtown city apartment, but was well equipped. It is just off of the square away from traffic, but is right above some restaurants that keep the noise level pretty high well past midnight. If Lisbon was it's usual temperature this would be fine because shutting the windows cut 85% of the noise, but given the heatwave going on while we were there, it made the rooms far too hot.
The back room is much quieter than the one in the front. We'd recommend ear plugs if you're anything other than a very heavy sleeper if staying there in the summer. None of this is the apartments fault (that's why we stayed where we did, we want to stay in a lived-in neighborhood), but just be aware so you have a good night's sleep.
The restaurant immediately beneath the apartment had fantastic fish, so we highly recommend that place (never learned their name). it's cash only so bring euros.
We greatly enjoyed Lisbon and would stay here again if we were back in Lisbon.