The Mob Museum was really great. We went to Las Vegas earlier this month and while looking for non-gambling things to do, my husband came across this. Our guys are not really the "museum types" so we were surprised to have spent 3 hours here and could have stayed a tad longer but we were bumping up against closing time on Saturday night. The people who worked there were really a hoot and added a lot to the general vibe.
The best part for us was reading all the mobster's monikers, prompting us to come up with some for ourselves which we are still cracking up over.
If you search online you can find a coupon for $2 off an admission, good for four admissions.
There is apparently another mob-related display at Tropanica - I think that one is called Mob Attraction so don't get confused by the fact that there are two.