This place is packed. I've been here a few times now, and the only downside to this place is that it's sometimes tough to get a ride back to the hotel you're staying at (assuming you took a cab to get a burger). One alternative is to run across the street to Wild Wild West, but that's definitely hit-or-miss.
As for the food, if you've had In-N-Out anywhere, then you'll know it's terrific (though while its similar to NYC's Shake Shack, its just a bit different/not as good). Lines here can get pretty long, but overall, the wait's not too long, and you are usually able to find a seat either inside or outside.