I've never done Iceland, but I've been on the Caribbean Princess three times with a fourth coming up next week, and I have always loved it. I feel like the Crown Grill is always better than on the Royal Class ships. It is a smaller ship but I don't feel crowded and I feel like they do crowd dispersal very well. It doesn't have Alfredo's but Slice is better than the Lido pizza on the Royal ships. It's not a bells-and-whistles ship but we're low maintenance. We only had one technical problem in those trips, and that was AC trouble a few nights on one sailing. We propped our balcony door at night and got a great sea breeze, didn't even miss the AC. But if we had complained I'm sure it would have been handled or compensated one way or another.
TLDR: I think the CB complaints are a bit overblown but everyone cruises differently and as different priorities. If you love the intinerary I wouldn't let the ship deter you.