I try to go to Hakkasan every time I am in Las Vegas. This is simply the best club in the city. This club usually charges a cover to get in, but you can sometimes go around it if you register on the guest-list online. Unfortunately, this is only possible on certain dates, usually when the best Djs aren't around.
The club's main area is very large, but it always gets very crowded anyways and particularly so on the Holiday weekends. The shots/drinks offered by this club are pretty pricey and you should expect to spend a significant amount of money on them if you don't have a table. The tables are also among the most expensive ones in Las Vegas.
The best thing about this club for me is that it usually has some of the best DJs on the EDM scene. I personally went to see DJs such as Calvin Harris, Hardwell, etc... and I have never been disappointed by Hakkasan. This is the ultimate club experience in Las Vegas.