I was genuinely shocked by how many artifacts from Pompei made it through. The museum has an EXPANSIVE collection. If you're someone that likes to read the signs and get as much as you can out of your visit, I'd say to allot 5 hours, at least. I focused on the artifacts relating to Vesuvius, and then glossed over the other parts of the museum, and it still took a sold 5 hours.
Take aways that were different than I had expected- there are no casts of the victims at this museum (and if there are, I somehow missed them, and I would be so bummed!) But what I got was a comprehensive overview of what life may have been like there. Any disappointment to not have seen the figures (victims) I'd initially anticipated seeing was replaced by an appreciation for how much more I know now about the life and culture of the cities affected by Mt. Vesuvius. When I go to Pompei tomorrow, I know that everything I saw today will make the ruins "come to life" and be a much more textural experience, rather than just seeing ruins and trying to take a guess at what life may have looked and felt like.
Aside from the impressive collection, the museum itself is a gorgeous building to be in- I didn't have a map, but it's sort of shaped like capital "I" and the halls that adjoin the wings on both ends are just stunning. There is a cafe, a lounge, and plenty of other opportunities for giving your feet, back, or brain a rest- including two gardens. I highly recommend this museum. The staff were all incredibly pleasant and helpful.
(Tip: The bathrooms are on the bottom floor)