We just did this itinerary on the Coral Princess this past January. While Princess is my preferred cruise line, I do not fit in their normal target demographic being late 20s. Having done several transatlantics, I'm no stranger to sea days. With that being said, I learned the Coral Princess is not the ship for me and I'm not sure I would return on the Coral or Island unless it was a very attractive itinerary and also heavily port intensive. I found the ship to be very boring with limited amenities and not much to do.
Also of great importance, the provisions used onboard weren't anywhere near the quality used in other parts of the world. The food tastes for similar menu items had varied greatly and the variety in the Horizon Court was also pretty limited. It was too many sea days for me, at least, on that type of ship and going forward, I'll be much more careful selecting ships. It wasn't my best cruise nor was it my worst -- I'd simply rate it as okay. Antarctica made up for some of the disappointment but we had only spent 2.5 days there instead of the 4 quoted on the booking due to weather delays and other various geographical constraints.
Antarctica is truly spectacular and the itinerary was fantastic -- you'll have a great time regardless being one of the very few people able to visit the region. If you have the chance to go, take it. If the cruise is underwhelming, it doesn't matter because you're going for Antarctica which won't disappoint. Just be prepared for the comments and shock you'll get when you say you are going there or have been there. If I were to go back, I'd opt for an expedition cruise and have an actual landing on the continent.