It’s an incredible experience. The hiding place is essentially as it was after the Franks and their friends were arrested and the place was emptied.
The museum has done a wonderful job of preserving the setting and providing the historical context so that you feel as if you were hiding from the Nazis yourself. There are also wonderful films of Miep Gies, Otto Frank and others who knew Anne.
They’ve also done a great job adding exhibits related to questions of freedom.
For the number of visitors that go through this small space, you don’t feel terribly crowded. If you go at midday, especially in the summer, you can expect to wait in a long line. Either go early or later in the evening.
Also, be prepared for the steep stairs. Like most of the old houses in Amsterdam, it is a narrow and tall building. Some of the stairs are more like ladders than stairs. There are only a couple of sets to climb, so an average person wouldn’t have any real problems, but if you can’t climb stairs, then more of the house isn’t accessible.
BTW, avoid the pancake house that is just down the street on the Prinzgracht. It is truly awful.