I'll start with the good - the Koningsdam is a beautiful ship! Out of all the cruises I've been on, the crew had to have been one of the friendliest and more willing to help out of them all. The food was great, music talent was amazing, floral arrangements were beautiful, cabin and bathroom were a good size (3 in a verandah room) and the ship was clean! If those are the only criteria you look for in a cruise, aside from the ports of call, then you will love this ship. But don't get your hopes up about having anything to do while onboard.
For someone my age (25 - 32 y/o range) - there was hardly anything to do, and I could count on two hands the number of people I saw around my age (excluding crew). My dad and I joked that we should've sponsored scooter races with the amount of walkers and scooters we saw onboard. We were shocked at how old the majority of guests were. One night at dinner our server even told us that the amount of scooters was low and is typically much higher and they have trouble finding places to park them in the dining room!
I missed typical cruise "activities": live band by the pool, contests/activities at the pool, karaoke, The Newlywed game, getting to see the mainstage singers/dancers perform more often (just to name a few). Daily activities included: bracelet making, floral arranging, trivia, and many computer seminars. You won't find the grand center of the ship with a grand staircase either.