Native Texan, allow me to explain.
Whataburger is basically the equivalent of Shiner beer.
It's in some grey area between being mass-market shit and a smaller, cottage industry product.
I've got at least three other burger places that are MUCH better than Whataburger, however, they aren't open 24 hours a day, nor are they either priced accordingly or accessible through a drive through.
I find it much better than Wendy's, both in terms of quality and quantity, but I really dislike Wendy's, both their burgers and fries. From a more objective view, they're maybe just a step or two above Wendy's, but not by much.
It's definitely a solid burger and it grows on you over time. Their other stuff, from chicken to shakes, is top notch for a fast food place, nearly incomparable.
It does suffer from overhyping because Texans are the loudest braggarts you'll ever meet. How can you tell if someone is from Texas? Don't worry, they'll tell you.
In-N-Out is far more overhyped. Five Guys is too expensive for what you get, though their fries are much better. Haven't had Shake Shack.
That said, there aren't many things I'd rather have than a No.2 with cheese, fries and a Dr. Pepper.
Also, Whataburger's breakfast is 11/10 and available from 11am-11pm - find me one place that has something half as good as the honeybutter chicken biscuit.