I LOVE Serendipity 3. I know that other reviewers are all salty about the long waits, the sometimes crappy service, the prices, etc., but I love it here. I have never had anything bad here (The burgers, pizza, and grilled cheese are great...I dream about that grilled cheese and tomato soup. Seriously.), the service has always been decent (even at the bar), the place is adorable, you can either sit indoors or out, AND you can choose to order from the restaurant or their takeout window. Of course sitting outside is hot (IT'S THE DESERT, PEOPLE!), but you get a nice view of the strip for people watching and you get sat faster. Plus? Food is always better with crazy people smack talking. Try it...I swear.
I always make a trip to Serendipity when in Vegas and you should too.