I think that's why I like it, too. We are also watching Killjoys, about some futuristic bounty hunters, and while I enjoy that one, it's definitely not as "serious" a show. Hard to call it light and fluffy, because there's quite a bit of violence; but it also includes more humor, and the characters are more formulaic. It's fun, but I definitely feel that The Expanse has more depth.
I will probably get tired of it at some point; I generally do with series that go on for any length of time. I never watched the last season of The West Wing; never saw the last episode of Season 3 of Sherlock; etc. Even though I loved those shows.