My wife & I were in SIntra for a week and were so impressed on our first visit here that we went back again on our last night.
We found Incomum on a fluke as we were looking for a much higher scale restaurant (recommended by our hotel) and got lost, but we were certainly not disappointed. The atmosphere is that of a local, pop-in neighborhood restaurant, but the only thing better than the food and wine was the service.
It is a relaxed atmosphere with small and close tables, but it was enjoyable feeling as though we were enjoying dinner in the real Portugal.
Between the four meals we enjoyed there, we got to sample plenty of what was on the menu. The vegetable soup was fantastic and the meals we had (beef, shrimp, risotto and cod) were all very enjoyable and accompanied by tasty vegetables. The side dish of the local bread included a cornbread which was incredibly different and delicious (so much so I ordered seconds on our last visit).
On both visits we had Catia as our server. She was so pleasant and very helpful in recommending a good local wine and explaining the dishes on the menu. She made sure our wine glasses were full and that we were happy with the dishes we ordered. She remembered us on our second visit and made us feel welcome and asked if we wanted the same wine we had the week before, which we found to be amazing that she remembered.
On our first visit we had dessert and the chef's own creation of tiramisu was unique and very seasonable and tasty.
All in all, the food was good, the service outstanding and the prices were very reasonable for what we enjoyed.
Incomum should definitely be on your itinerary when you get to visit Sintra and be sure to ask for Catia, you will also be impressed!