Luv-It is a must stop on any Vegas trip. It is as good as people say, it is worth going out of your way for. It is pure heaven - it cannot compare to ice cream or fro yo.
My favorite thing to get is the Western. It comes with hot fudge, caramel, and pecans. A cherry and whipped cream are included if you get the regular size ($5.25), that stuff doesn't come on the junior ($4.25). The junior is more than big enough for a normal person, so only get the regular if you want to truly indulge, or can handle your sweets.
It is kind of soup-nazi-ish ordering. I've always been too scared to get anything but vanilla - the standard flavor everything comes with unless you tell them differently. Once, a friend asked for whipped cream and a cherry on his junior sundae - it was the equivalent of George asking for bread in Seinfeld. Scary.
As long as you follow the ordering procedure (outlined on their website), you'll be fine. And, like the soup nazi, the deliciousness of the custard makes it all well worth it.