My husband and I and another couple sailed on the Norwegian Star's 9-day Baltic itinerary (which sailed from Copenhagen and included ports in Berlin, Tallinn, St. Petersburg, Helsinki, and Stockholm) in July 2014.
To be honest, we were a bit nervous about booking on Norwegian. We had never sailed this line before (but had sailed Princess and Royal Caribbean), and reviews on Cruise Critic about this ship were very mixed (from "we loved it!" to "worst experience ever"). However, our travel dates were a bit inflexible, and the price was appealing, so we took a chance. And we were really glad we did!
The negatives that we were very worried about that ended up not being that negative: