It's rare you see a show based on a book series that improves upon what the original author created.
It's even rarer that you see a show that improves upon what the original author created, while following the author's vision to the letter.
The expanse takes a great book series, and transforms it into an excellent show, all the while never once betraying the original content. That is an incredible achievement, one you find so rarely in entertainment.
Cool things:
-well-researched sci-fi: the universe is 100% believable. I love star trek, star wars, but there's no voodoo magic here. Real physics, real technology, real weapons. The only exceptions are used to drive home the sense of vastly superior technology, but it's well-executed; that gap is never attempted to be explained with wishy-washy smart-sounding bs.
-well-casted characters. Amos and Avasarala stand out as actors fully able to portray their complex characters. Holden is well-casted to be well, Holden. His character is fairly one-dimensional, but it's made clear his character is the bland moral paragon and this is used as a tool to make the show more interesting as this comes into conflict with the complex moral framework of the show.
-gorgeous. the CGI is top notch and paired with the excellent music is good enough to send chills down my spine. Almost every scene is good enough to be used as a wallpaper for your computer and the animations are high-budget.