The last time I went to an In-n-Out I wasn't as impressed either. Not sure if its because my taste has changed, or the food changed. When I went to one a few years ago it was much bigger with more menu items. And indoor seating.  When I was a kid and the local place opened, it was just drive-through or walk up to the window. If I remember correctly, the only menu items were burgers, fries, soft drinks, and milk shakes. You could ask them to grill the onions on the burger. It was SO good!
Simpler is often so much better. When places try to satisfy requests to add more variety, the quality seems to change.