I visited this WHS in August 2014. I spent 3 days here and I would have loved to stay longer. The historic centre is packed with sites to visit through narrow streets and alleys leading to several squares and eventually down to the waterfront by the Douro river. The rest of the city is falling down to pieces and decadent at best although I agree that this helps to have an authentic overall experience. The best viewpoints are to be found at Vila Nove de Gaia by the waterfront, in front of the monastery or on the funicular. The Igreja de São Francisco should not be missed as it has a unique interior and a beautiful courtyard full of azulejos. Other churches worth visiting for their azulejos exterior are the Church of St Nicholas which is just opposite the one of St Francis and the Church of the Holy Trinity. Oporto is a vibrant city and also the best place to go for a long day trip or 2 day trip to take in another WHS, the Alto Douro.