I've always loved black holes and I've always wanted to read Asimov, but I never realized how well the two would go together.
It's extremely approachable, for the content concerned. He writes a lot like Sagan in that -even though astronomy requires a ton of math- he simplifies it and mostly states it in comparative terms like "1.4 times the mass of the Sun" rather than "2.7846 × 1030 kg".
The best part about this book, for me, wasn't even the black holes themselves -it was everything else leading up to it. I learned so much about the elemental forces, the formation of stars, and every different type of step of ending a star can have. And what I love most it got down to the subatomic level and was still completely understandable.
The only thing that was a slight disappointment was that the book became less and less sure as it went on. Really almost all of it was known fact until you got to the topic of black holes where it became much more of a "what if?" game. I can't blame Asimov, however, as he's just reporting the science and it was still entertaining and informative to read.
Maybe it's because it is a subject matter that interests me but I couldn't put this book down. Asimov is on par with Sagan for making science fun but informative. Even though I'm sure there's been more discovered on the matter, I think this book makes a fine introduction to astronomy.