I could only imagine how hard it is. I, myself, am horrible at portraits of humans. I think it's amazing, and very well done, but there's something that makes it not quite look like Beyonce. But yes, very nice. One of the best I've seen!
I think it is her nose. The shading that comes out of her eye that defines the shape of her nose is off. Maybe bring that shading down and out a bit and change the right nostril to redefine her nose. I'd have to look at the photo, but I'm usually pretty good about picking up on those differences. Otherwise, looks pretty good! I really like it And I just realized this is a year later, but oh well