after watching the opening credits sequence, you'd be excused for mistaking The Expanse for a sci-fi knock-off of Game of Thrones. Heck, it's pretty clear SyFy wants you to mistake it for a Game of Thrones knock-off. The first episode doesn't really live up to that bill, though.
First, there are way too few characters. It becomes fairly obvious that we've got three main characters. Miller is a “cop” who actually works for a private security firm that does the cop-like work on the colonized asteroid Ceres. He's all noir, with his hat and clothes, his tough-guy demeanor and his dialogue that feels like a washed-out imitation of Dashiell Hammett. He's a “dirty cop,” though the implication is that, being a private corporation rather than a public service, the entire organization is on-the-take. We're also supposed to get that he has a heart of gold because he feels guilty about things and then gets ugly-violent about it later.
Jim Holden is one of those characters who's supposed to be mysterious. He's clearly running from something, clearly inhabiting a social and professional level below his actual birth and abilities, and clearly wallowing in (rather tame and mild) hedonistic delights to distract himself from the previous two aspects of his character. He also holds a vague position of authority on an ice-mining ship, doesn't want to advance in rank, and is banging the navigator who is the only other person on the ship who grooms and talks like lawyer instead of a factory worker. He's so generically mysterious he's boring, because you know you can't invest in his character. Luckily, he's surrounded by far more interesting people, and being “mysterious” means he can engage in broad swings in style and tone, allowing him to take plot-necessary actions nobody else in his position would sanely entertain.
Finally, we have Chrisjen Avasarala, an Indian grandmother who wears elegant saris, tickles her grandson, and, as Undersecretary of the United Nations, tortures political dissidents, possibly to death. Like Jim, she's such a different person from one moment to the next that it's impossible to invest in her, but unlike Jim, she's not surrounded by more interesting people. What you'll be paying attention to when she's on the screen is the spectacle of wealth and power and future Earth around her, and the vaguely Tarantino-esque threat of sudden, explosive violence that seems to linger in the background of every scene she's in.
Babylon 5 than it does to Game of Thrones, from its grungy blue-collar focus to its Cold War themes and hidden motivations. You'll also see a lot of Babylon 5 in the space scenes, where ships move like physical bodies in a Newtonian universe but we still hear the rumble of engines as they pass by the camera. The sex is fairly tame (there's a single scene of gratuitous zero-g sex between a man and a woman), the violence isn't very graphic (though it does aim for a certain emotional impact that it doesn't always reach), and the spectacle is a bit too industrial grunge to really pull off the whole GoT-in-space vibe the marketing team would like you to assume.
It's also very much a modern serial show. You can tell they've got stuff plotted out pretty concretely (the story is based on a novel series) and look forward to a slow, leisurely reveal. Also like modern serial shows (and again, very much in the vein of Babylon 5) they love to set up your expectations and then pull the rug out from under you. They do a fairly masterful job of that right up near the end of the first episode.
Unfortunately, our three main leads do such a bang-up job of being mysterious and unpinnable that its really hard to invest in them as a viewer. (There's actually a fourth key character, but you see so little of her that you'd be forgiven for having entirely forgotten about her as the closing credits roll.) If the show is easy to watch (I don't have cable, so that means episodes posted online) and I have time, I'll probably catch the next few episodes to see if it grows on me; I'm at least that intrigued. But I've not seen anything yet worth rearranging my schedule for. On a scale of one-to-five stars, I give it a tentative three stars.