Hundreds of years into the future, Earth has colonised Mars but Mars is now independent, and the two planets are in a constant state of distrust and unease. Caught between these two are the people of the asteroid belt and outer planets. James Holden, the executive officer of a freighter witnesses his ship, being destroyed by what appears to be a Martian warship. This heightens the tensions between Earth and Mars and sets Holden and his remaining crew on a quest across the galaxy to find the truth behind the incident. Meanwhile, on Ceres in the Asteroid Belt, a police detective is searching for the daughter of the wealthiest man in the galaxy. These are all parts of a conspiracy that that will threaten life in the Solar System.
Brilliant. I am not a huge fan of sci fi series (Firefly was the notable exception): they tend to rely too much on gimmicky inventions and faux science, at the expense of plot. The Expanse is different: the science and future history are incredibly believable. I'm no physicist but I found it difficult to fault the physics and technology involved. More than that, the futuristic nature of the series provides the background, not the story, so the series does not rely on it.
What the series does rely is plot, and it is a great one. Starts out pretty slowly, so doesn't immediately pull you in, but after three episodes or so it is off to the races. The seemingly-parallel stories start to intersect, things start to make more sense (though, thankfully, not so much that the mystery disappears), the characters become more interesting and the action ramps up.
The story is then intelligently developed over the next three seasons. Despite the many twists and turns, the plot remains solid, with no twists for twists sake and everything fits together very well. Even when one mystery is solved, another emerges to take its place, without feeling gratuitous.
Quite grittily told too: no characters are unexpendable, making the plot quite unpredictable.
Superb special effects and action scenes. The CGI is absolutely seamless and realistic, without being too ostentatious. Like the science, the CGI is the medium, not the message.
Performances are where the series does feel a bit lacking. The main characters - the crew of the Rocinante - are reasonably well played, though there are no stand-out performances. Some of the lesser characters are quite badly played though, with the worst culprits being Shohreh Aghdashloo as Chrisjen Avasarala and Shawn Doyle as Sadavir Enright. Any scene they were in made me cringe, with Aghdashloo being particularly irritating. She wasn't helped by her character being pretty badly drawn, with the worst dialogue and most grating mannerisms of any character in the series. The two factors - the character and her performance - just compounded each other.
The lack of character depth is a general weakness in the show too. The series is about the intrigue and action, much more than the people and their relationships, making character engagement less than complete (unlike Firefly, which was highly engaging because of the characters and their interactions).
This is a minor flaw though, as the plot and its roller-coaster momentum propel the show.