I sailed on the Sun last week. The crew is great, the ship is well maintained, but compared to newer ones, beginning to seem small and dated in layout and amenities. Nothing bad though, just not all the new bells and whistles. Big plus is the Great Outdoors area of the buffet, newer ships don't have that and it's the best place to eat!
The only advice I'd give is avoid any cabins aft of the rear stairs/elevator. The ship has some sort of ventilation issue and it stinks. Our aft balcony smelled like sewage most of the time.