A friend and I recently finished hiking the Camino Portuguese, started from Lisbon in mid-September, I just got home yesterday. Most people who talk about hiking the Camino Portuguese start from Porto or perhaps Tui, but we did the longer version starting in Lisbon.
Overall, I understand why people start from Porto --- it's not just those who can't or don't want to hike the longer distance. There were certainly good parts between Lisbon and Porto, but overall more road walking of the type where cars are driving by and more built-up portions. From Lisbon initially of course there's some of that, but I remember the last couple of days into Porto as having pretty much no places where you weren't walking by houses on roads. It wasn't "bad", but all things being equal I don't particularly recommend the part from Lisbon to Porto. The beginning of the day going out of Porto wasn't all that great either, but from then on it was good. One thing, however, about the Lisbon to Porto portion --- very few other pilgrims on the route, Albergue's pretty empty. Though also less Albergues and farther apart so less options there. Still, somewhat of a shock to the system when we started encountering all sorts of just-starting pilgrims after Porto.
On the upside, food in Portugal is particularly inexpensive, which was nice and the Portuguese people are great, and again --- after getting out of Porto, this more commonly walked part of the Camino Portuguese was nice.
While we had done so once before, we opted to continue hiking after Santiago to go on to Muxia and then Finisterre (both on the western coast), and this is all good walking in Galicia, good weather for us too. In fact, it didn't rain on us once while we were hiking the entire trip, great weather really. Except that this was getting into drought conditions, Spain/Portugal went through 50 days of no rain, and some forest fires were reported burning pretty close to parts of the Camino that we had recently walked through (Pontevedra, Caldo de Reis). All part of the adventure, I guess.
My trail blog for the trip is at http://www.postholer.com/brianle