We were on the Poesia's inaugural cruise (April 6th - 19th; London (Dover) to Venice. I was interested to see the member reviews here as well as the comments on this board. Most of the complaints seem to be about the food while the ship itself got generally high marks.
I'm writing this primarily as a ship review, but I will briefly go through the ports (I loved them all): • London - We spend two and half days here before the cruise. It's a beautiful city with so much to see in the way of history and architecture. We particularly enjoyed the British Museum. Excellent mass transit system. • Cork/Cobh Ireland - Scenic, friendly, nothing specific I'd describe as a must-see. If I did it again, I think I'd spend more time in Cobh (where the ship docks) and less in Cork. • Lisbon - I loved it. I would definitely like to go back. Friendly and helpful people. Beautiful stone and tile work everywhere. We enjoyed the Castle and the Jeronimos Monastery. • Barcelona - Attractive city. Nice parks. You have to see the Sagrada Familia. • Rome - I wouldn't know where to start. I think the must-sees in Rome are known by all. St. Peter's Basilica was amazing. • Naples - Naples, at least in the midst of its current garbage crisis, was not pleasant. I'm sure there are things to do and see there, but our experience was limited to walking through the city to the train station where we caught the Circumvesuvius line to Pompeii (wonderful) and then on to Sorrento (gorgeous, one of my favorites). • Messina, Sicily - Our time here was also limited to walking to the train station where we caught a train to Taormina. Unfortunately we didn't have much time there and found out only too late that we had gone to the waterfront when the main town was high on the hill above. • Dubrovnik - A lovely city. The main attraction is the Old City, but the whole area is beautiful. I want to get back there someday for a longer visit. • Venice - A place everyone has to visit at least once. We stayed 2+ days there and really enjoyed it. Just roam the streets and take it all in. Piazza San Marcos is a must see. Get a Water Bus pass for the duration you're going to be in port - it's a fun and easy way to get around. Aside from the main island, I would also recommend going out to Murano (glass!) and Lido.
We saw all these ports on our own. We gave up on ship-offered excursions after about our second cruise having found them to be overpriced and over-restrictive. While we made significant use of public transportation (which, compared to Seattle, is outstanding everywhere we went, with the possible exception of Dubrovnik), mostly we saw these ports on foot. I would recommend that method to anyone with the energy to do it as the best way to get a real feel for a city when you are only there for a short time. It also helps work off all of those cruise calories.