In order to maintain consistency, Starbucks roasts their coffee a tad bit longer than many might prefer. The espresso you get in New York is going to taste exactly like the one you got in Hong Kong, or New Delhi - that's actually kind of impressive. Still, if you're someone that likes their beans just past the second 'crack' - you might find their espresso a bit too dark, a bit too bitter and a bit too expensive to be accepting of a disappointment.
Now, the coffee that they sell in bags gives you plenty of options - you can still get a nice blonde-roasted bag of single source Arabica at many locations. If you're there to order something with milk in it, then you're probably not going to notice just how dark the beans really taste - you'll probably just enjoy your coffee.
However, if you tend to take espresso straight, or a drink that is basically espresso cut with water or very little milk, you might thumb your nose in the air a bit. Then again, I'd take a bitter-ish espresso over a cup of bland-ish drip any day.
People love to complain if given the opportunity. If you like their espresso, enjoy it - if not, well, drink other espresso :)