Of the large craft breweries in the United States I rank Sam Adams as one of the top 5 for sure. I think Sierra Nevada has a better taste, and my favorite large-scale craft brewery is Saranac (brewed by Matt Brewing Company.)
The answer to whether Sam Adams is “special” or not is kind of hard to answer. As someone active in the beer drinking scene, some people (unfairly) tend to automatically assume only the smallest microbreweries and brewpubs can have truly good beers. Under that criteria, large craft brewers like Sierra Nevada, Sam Adams, Matt Brewing Company, Magic Hat etc will not fare well, as all of them ship hundreds of thousands of barrels a year.
Another criteria people often use is basically how “unique” the beer being brewed is. To give you an idea of what you mean, at my local grocery store you can get beers from very small microbreweries with flavors like “Banana-Nut Bread”, “Bavarian Chocolate Pie”, “Cranberry Wheat” and etc. Some of these are interesting to taste because they sort of defy what you would normally expect from a beer. A lot of these beers will sell for like $8 for a small bottle, or sometimes $15 for a 4 pack of bottles.
Personally while I think those “unique” flavored beers are interesting and show real creativity, and can be fun to try, I really prefer a beer that tastes like a beer. A traditional dark lager, pale lager, pale ale or etc done very well typically is something I’ll like more as my “regular beer” than I will some crazy-flavored beer that is trying to “shatter barriers” by infusing fermented beverages with strange flavors.
Under that criteria, I won’t say that Sam Adams is the best in class for lagers or that Sierra Nevada is the best pale ale, or Saranac has the best IPA but for widely sold beers that you can order in many restaurants I think they are as good as it gets. There’s better stuff out there, but none of it that I’m aware of that you can reliably buy at any restaurant or bar when you’re traveling. There are locally brewed beers I will prefer, both near where I live and beers local to other areas, but for widely distributed beers I think it’s hard to beat the aforementioned craft breweries.
I also should give a nod to America’s largest brewery (although not a craft brewery): Yuengling, their product is essentially what I think Bud Light or Miller Lite would taste like if they were good beers. So it’s not exactly a connoisseurs beer, but it’s a traditional cookout type beer in the same vein as the stuff A-B or Miller makes but significantly better.