The Mob Museum is a must see. It is newish, and it's a sister to the Spy Museum -- the operator converted to non profit, so concerns about that aspect of the entity are lessened. The former mayor of Las Vegas, a "mob lawyer" before that, came up with the idea. It's quintessentially of the place.
The exhibits are thorough, thoughtful, and just on the right side of gruesome and lurid ny standards. There is quite a bit of discussion of Hollywood glamorizing organized crime, which is a morally appropriate intervention. There also is as expected quite a bit about Las Vegas as a city built by the mob, literally and figuratively.
Here is a question for which I have no good answer. Would it be better or worse, descriptively and normatively, if the exhibits featured more of African Americans, Hispanics, and Asian Americans -- and women? Apparently Italian American groups protested the concept of the museum. It is very heavy on people of Italian descent, with some Jewish representation. There is a tiny bit about others.
Anyway, I do not hesitate to commend this as a must see in Las Vegas. I would go at least once, and if they did more events or had a special show I'd go again.