I, like some others here on Yelp, have yet to try the original NYC location(s) so I don't have anything to compare this one to yet. That being said this is what you should know:
Do be prepared to wait (and in the Vegas summer heat this can be a little unpleasant)
Do order the frozen iced chocolate (it's one of a kind)
Do be prepared to shell out some money. This is a famous and touristy spot on the Strip so like anything else, it's a little pricier than most places
Do try the food, they're known for their desserts but the food is quite good too
Don't get upset...the wait will be worth it
Don't forget to look at their intricate menus, they are pretty cool and tell the story of Serendipity in NYC
Don't be fooled by your waiter's selling tactics. They may "conveniently" forget to mention if you order candy, etc with your frozen hot chocolate, it's going to cost more
Keep all that mine and you will enjoy your experience at Serendipity.