Stacy P.
Yelp
Again, this is something you should make time for, particularly if you have the Museumkaart. With the card, admission is free.
The church is, of course, beautiful. You'll be able to appreciate the masonry and grand organ as you walk around. And, make sure you head over to the far side of the church to pay your respects to Saskia, Rembrandt's wife. Her stone is well marked and easy to find.
When I visited they had an interesting exhibit about the end of relationships. People had submitted letters, items, photos and a letter describing their love affair, and how it ended. It was surprisingly interesting, and sometimes moving. I've read through the other reviews here, and they mention fashion exhibits, etc. So, it seems no matter when you go, you'll have something to look at in addition to another grand organ.