Hey, a burger thread! (Thanks for splitting this off, VF!)
So my take on In-N-Out is basically this: The burgers, at many locations, are probably the tastiest burgers out there. The problem is that some locations have bland burgers. I'm almost certain it has to do with location-by-location policy with regard to how much salt they add to the burger on the grill. Don't add enough salt, the burgers are bland. I would say that I have enough experience with about...7 different In-N-Out locations throughout California to pass judgment, and 5 of those 7 I will happily go to. One of them is marginal at best, and one of them I will simply avoid unless somebody else wants to go there. The real draws on the burger are the meat, the sauce, the glorious, glorious processed-cheese-food-stuff (like, seriously, best, thickest cheese on a burger anywhere, hands down) and the sliced (not grilled) onion. The onion is also pretty variable, but this doesn't seem to be related to location - but when it's nice and pungent, with the meat cooked right, yeah, that's the best chain burger out there at any price.
The fries are not worth buying. They're edible, but they're pretty much my least favorite fry. On the bright side, they are consistent. Many fast food joints will drop a stinkbomb of a package of fries on you 10% of the time, but with In-N-Out I've never seen that. Still, my M.O. is to skip the fries altogether and just get two cheeseburgers instead (sometimes a double-double but I actually like the bun/onion to meat ratio better on the singles). I can't really speak to the shakes as I'm not a fan of shakes in general.
Yes, In-N-Out burgers are small, but that is offset by the fact that they're also quite inexpensive. I don't think you get a whole lot more meat (if any more) on a Five Guys burger that costs twice as much. Sure, Five Guys has a lot more topping options, and it's a good burger, but it doesn't reach the marriage of value and simplicity that In-N-Out hits.