Love Five Guys, but to be honest, I can't pinpoint why. They don't have the best tasting bacon (that goes to Corner Bistro in NYC), they don't have the best burger, nor the best bun, but somehow, the end burger is much better than the sum of its parts. It is by far my favorite burger chain.
I read the OP and had the exact opposite reaction... I tried In and Out well before I tried Five Guys, and though, this is it? Very big letdown. I would have preferred a McD's burger 5 times over to In and Out. To be fair, though, my wife liked the In and Out (but she likes Five Guys a lot too).

I'm so-so on the fries at FGs though. When they are cooked crispy, they are great, but most of the time they are pretty soft and I am not a big fan of the fatter, soft fries style they use. I prefer them thin and crispy.