I have had a few issues with the Cosmopolitan and it's music venues. Parking is a major problem here. They have limited space, so arrive around 5pm to be secure of a parking place. Arrive at 6-7pm you risk getting turned around.
Even then I would suggest park next door at Aria/City Center. A lot more parking and just a 5-10 minute walk which will be faster than parking at Cosmo.
I don't want to go in to various ticketing/seating/line issues here.
I will say they have solved many of the early problems they had which showed they didn't know what they were doing.