The Mob Museum is worth visiting at least once. You don't get to see a museum of this type often in the world, namely, a museum talking about gangsters, how it started in the USA, how law enforcements, intelligence, and government handled it in the past with some real examples. Washington DC's Spy Museum has a bit of reminisce. They are both good and educational museums to visit.
The museum used to be an old US post office, a historical landmark. You can purchase tickets online or on the spot, the process was easy and straightforward. Staff were all friendly and helpful in providing directions and answering questions. The self-guided tour/visit starts from the third floor, and you work your way down to the first floor. They also have guest speakers who used to be part of the gang members to speak, the information desk can share the schedule, as it varies daily. They also have optional interactive experiences which you have to pay extra for. I did not have time to participate, so can't comment on them.
It's an informational, educational, and interesting museum. It's located within walking distance of the Fremont Street in downtown Las Vegas area. There is a parking lot right outside and a parking garage across the street.
Budget 3 hours so you are not rushed if you want to see and experience everything thoroughly.