Having eaten and enjoyed Shake Shack since they first opened their Madison Square Park location, I can definitely understand the hype and the mixed reviews.
First of all, they're not playing in the same market segment as McDonalds or Burger King. A closer comparison would be the premium / fast casual segment such as a Triple O's or even Butcher Club.
Back in the old days, they were using nearly the same Pat LaFrieda blend (80% brisket with short rib and chuck making up the rest) that they used at the Spotted Pig and Minetta Tavern which were charging 5-6x of a shackburger. So at that time, eating at Shake Shack was an affordable luxury.
Since then, I don't think LaFrieda has the scale to keep up with their massive demands but they've still kept quality tight and supply chain surprisingly effective. But nearly all locations I've eaten at (Tokyo, HK, Seoul, Las Vegas) the produce is fresh, the burger well cooked and seasoned, and the bun (the original uses a Martin Potato Roll... I don't know what they do for the Asia product) reliably squishy and slightly sweet.
Shake Shack was founded by Danny Meyer, who in the restaurant world is synonymous with customer service and experience. Whether it be his high end restaurants such as Eleven Madison Park (no longer owned by Meyer but I ate there several time under his watch and the meal was worth every penny) to a lowly hotdog at Shake Shack, the customer experience is enjoyable. Although mileage may vary depending on the queues.
Side note: there is a famous story about Eleven Madison Park - several years ago, a waiter overheard a patron talking about how much they loved Shake Shack's burgers. They notified the service manager who ran across the street to Shake Shack (both EMP and the original Shake Shack are spitting distance from each other), and delivered to the customer a surprise intermezzo of a Shack Burger in the middle of his $225 USD tasting menu. These "surprise and delight" experiences are what creates lasting legacies (and is sorely missing from Hong Kong restaurants).
This is not meant to be a defense of Shake Shack - everyone's tastes are subjective. However I think it's important to understand the context and history of a dish or a restaurant no matter the provenance.
tl;dr: Home sick New Yorker mansplains a $6 burger to the interwebz
edit: A stellar recipe (for which I was a lucky taste tester during the development and refinement: https://www.seriouseats.com/recipes/...er-recipe.html )