It's a grand house, but small enough and well designed enough that you can feel you might like to live in it back in the day. That contrasts with many such houses that are too grand and over the top, those don't seem inviting. We didn't learn the somewhat tragic history of the family until after our visit - please look that up in advance, as it added to our appreciation of the house and its contents. Moreover, we were assuming it was just another rich banker, but we found there was a lot more to the family's story.
Plan on about 70-90 minutes here. Ideally you can access via the Monceau metro stop and have the short but beautiful walk across Parc Monceau on your way to the museum.
We didn't do the audio tour so the details of furnishings escaped us, but we enjoyed them overall. The china sets from 1700s in particular, amazing to see.
It was not busy, we arrived around 11-11:30am without any advance reservations and paid onsite, none of which was a problem. No lines at all, so you can keep yourselves footloose and avoid pre-booking this one but just show up.
Be sure to use some of the restrooms on various floors by the staircase, each of these feels like a step back in time, and we were impressed they are still allowing visitors to use their somewhat historic feeling bathrooms.