This is a great experience for tourists and locals!
The museum is within the old Vegas post office/court house, so it's really cool that they put it in a piece of Vegas history - typically the city just knocks down the old to make room for the new. They tell you it takes about 2 hours to get through, however if you really get into it and want to check everything out, it can take up to 4 hours.
It's a very engaging experience - with kiosks you can interact with, to showing short documentaries on key people or events that took place. If you have any questions at all, the staff is well versed with everything in the museum and are super nice.
On top of the cost of your ticket, the museum parking lot is $5. If you're trying to save a little, park in the "old bus terminal" parking lot on the corner of Stewart/Casino Center at no charge. (right next door to the museum).