We traveled as a group of 4 in our early 30s. For my husband and myself, it was our 4th cruise (2 Carnival, 1 RCI). All of us have been to Europe several times for land-based vacays.
I know I'm terribly late in posting this, but I figure that people are probably right now planning their Baltic cruises for this summer so it might still be useful. If you're just considering booking this cruise, DO IT! It's great.
The ship: The ship is nice. Well maintained and all that. Less gaudy than a Carnival ship but laid out similarly, which we like (except for the decks that you can't pass all the way through on, but it's not that big of a deal).
The cabin: It was fine. The shower was much bigger than we'd seen on other ships.
The food: It was really good! We didn't even go to any of the specialty restaurants because we were so pleased with the options in the dining room. This was especially delightful after having bad food on RCI's Splendour of the Seas in 2008. It was like an improved version of Carnival's food, which we'd liked.
The service: Like the food, this was a bit better than what we'd seen on Carnival (which we really liked) and far superior to what we experienced on RCI. Everyone was cheerful and very attentive.
The entertainment: The comedians were great! We were really impressed. We didn't especially enjoy the shows, but we've never been impressed with that sort of entertainment on a ship.
The partying: Oh boy, if you like dancing, bring your dancing shoes! There was dancing in at least a couple of venues every night. Take ballroom lessons if you want to take full advantage of this. It was super fun.
The casino: Our guys seemed to like it.
Other passengers: We met a lot of super nice ones. I'd say the average age was probably upper 50s/lower 60s, and there were only a couple of kids on board. Although we were 4 of very few 30-somethings on board, we had a blast with the other passengers. We did get a bit irritated with groups who don't understand lines, but that's obviously a cultural thing and really no big deal if you go in knowing that it's a possibility. If that sort of thing really bothers you, I'd recommend avoiding European cruises altogether.
I'll briefly review the ports below, but check out my blog - feistync.wordpress.com - for pictures and the specifics of what we did. Based on this cruise, we *definitely* plan to cruise with Princess again.