Smashburger has the BEST fast-casual hamburger, period! Their burgers are so delicious and flavorful and there are so many yummy toppings to choose from so you can make your ideal, personalized hamburger (avocado, bacon, cheddar, grilled onions on a pretzel bun... YUM!).
I don't get people who say it's expensive compared to a place like In & Out- of COURSE it's more expensive than In & Out. In & Out is a straight-up fast food hamburger. Smashburger is on the border between a fast food and a restaurant burger; the two cannot be fairly compared!
I ate here a bunch of times when I lived in Illinois and since moving to Vegas, I've gotten to try the Sin City burger (with a couple of modifications) and it was delicious. OH and the Smashfries are awesome. Salty, but awesome.