Undeniably one of the most popular and entertaining clubs in town, it is only for those with club-going encoded into their DNA. Why else would anyone pay this much, stand in lines this long, and have to deal with an attitude this severe? But club afficiandos are used to that kind of stuff so if you can stand the heat this is one of the hot spots you're going to hit.
Made famous when it was featured in MTV's Real World Las Vegas, Rain is a classic nightclub in just about every way, which is both good and bad depending on your viewpoint. The competition to get in and to be noticed once you do is as fierce as the beats the (often famous) DJs throw down. If you wear anything but your sexiest, in-season outfit you will probably not get any attention from anyone.
Having said that, if just going to dance and have a good time is more important to you than being noticed, this is a great club to do so at. The dance floor is large enough that you can actually find a little bit of square-footage to bust a move and the lighting, sound system, and special effects (which involve pyrotechnics and water) are eye popping.
I personally think there are better clubs in town but Rain is a classic and true club afficianados should visit it at least once.