Whataburger is just fine. Fine burgers, fine fries, fine shakes. but nothing earth shattering. I think it gets such loyalty because it's a regional chain, but if there was a Whataburger in every city like McDonalds I don't think people would make such a big deal out of it.
I know lots of people who visit California and immediately go to In-N-Out, can't say the same for Whataburger.