Our favorite excursion on the Sun was the Tracy Arm tour. The Sun does go up into Tracy Arm, and there is a good view of South Sawyer Glacier. However, we also got to see North Sawyer Glacier from the catamaran, which I don't think people from the Sun saw, as well as getting much closer to the face of South Sawyer Glacier.
While we were there in June, there were LOTS of harbor seals on the floating icebergs in front of South Sawyer glacier. Apparently they go there to mate and give birth, and the icebergs protect them from the whales. We saw a couple give birth, and several slide off the icebergs and go swimming. I don't know for sure if they will still be there, or if it was more of a seasonal thing.
We also saw 3 or 4 humpback whales on our way, and as mentioned, they idle the ship so you can get as close a view as possible. We saw 2 of them dive, and got good video of the tales going into the water.
We enjoyed the trip so thoroughly that we were really puzzled by some of the other passengers who complained about the cost, when all the Sun passengers did get to see much of the same scenery, even though at more of a distance. To me it was well worth the cost, but I guess not everyone felt the same way.