Got off the boat yesterday from the Baltic 12 nighter. We had 4 days at sea and never got bored. For the kids, there's always movies, the clubs, animation classes, eating, and just chilling out. Believe me, just chilling out is great after a few port days. About half our day at sea time was water friendly, especially in the afternoon. All 3 pools were nicely warm, and the hot tubs were actually hot at times. We had some rain, but not bad. The adult pool area was wonderful. Nicely sheltered, and the pool water was as room as some hot tub water I've been in. I also had a nice workout in the fitness area every day, saw a few movies, took in a few classes, vegged out by the Cove Café, napped, and then got ready for dinner and the nightly shows, which were all great. There's also several movies at the same time in your state room TV, including the latest Hobbit movie, etc . . .
If bored, it won't take much to find something unique to do. One afternoon, my wife and son wandered the halls for a half hour or so looking at how all the doors to the cabins were decorated. Very clever, and helped with burning off the food.
Being a little bored, by the way, is not a bad thing. We're too plugged in most of the time, and it's truly nice from time to time to just relax and have nothing to do but people watch. With that being said, even a Type A like me found plenty to do on the sea days.
Also, Talinn is fabulous. Of all the ports, that's the one I would really like to see again.