We have sailed several times - most on NCL. We always select interior cabins because our goal is to spend as little time there as possible. We have been pleased with NCL in the past. In fact, our favorite cruise was a full transit Panama Canal cruise in 2009. However, this was our worst cruise ever and fr at least two reasons:
Embarkation, ports of call and debarkation were all "okay". Nothing to be blown away by but certainly adequate. Embarked from Venice, visited Malaga, Lisbon and Puerto del Gado. Even the very rough seas during the crossing was acceptable because the captain worked hard to avoid rough seas - unsuccessfully.
What disturbed us was that entertainment was very minimal and the quality was very poor. We have never been bored on a ship before this trip and we can no longer say that. I have never played so many games of cards with my wife as we did on this trip! Crew seemed to have too much to do to be bothered with keeping the passengers busy. WAAAAY boring!
Have been to Venice before so didn't spend any extra time there.
Had also spent time in Lisbon before so took the stop and go bus around the city.