Novels that take place as humanity expands its presence in the galaxy are perennial favorites. (See previous post on Catherine Asaro's work as well) I've come across several contrasting and vastly entertaining series in this subgenre lately.
Fans of The Expanse (one of the most well-reviewed series on t.v., which was recently cancelled by Syfy and subsequently saved by Amazon) will be glad to know that it is based on the novels (Orbit Books) by a team of two writers under the pen name James S.A. Corey. Both the show and the novels are fantastic. In my case, since I began seeing the show before reading the novels, the two have melded in my mind in a very pleasing gestalt. Leviathan Wakes is the first of the series. The crew that comes together in the ship Rocinante are the first that remind me of the Firefly crew in their likable motleyness and unity. In this first novel, the point of view shifts between the idealistic Holden and Miller, the hard-bitten detective, a contrast that works very well. My one criticism is that the main female characters, Naomi and Julie Mao, are idealized to a point and not allowed to be totally human. But that's a common issue in sci-fi, I find.
A series that contrasts well with Corey's rather dark and militaristic vision, is Becky Chambers' The Long Way to a Small Angry Planet, which Tor.com describes as a "joyous, optimistic space opera."
The debut novel has been followed by two more, one just published, so enjoy! Her novels have attracted much attention and awards for their quality and different approach. Her emphasis is on the characters and their emotions.
In between these two series, as far as tone and ambiance, I would place Martha Wells' (read EVERYTHING she's ever written, not just this series, you will not regret it!) Murderbot Diaries novella series, the first of which, All Systems Red, just deservedly won the Nebula and Locus awards. In this four-part series, we get inside the mind of an AI security unit that goes quietly (and then not so quietly) rogue. The last novella in the series will be released in October.
On a totally different plane, is the hilarious, quirky Union Station series by E.M Foner (this interview by K.C. Sivils will tell you much of what is different about the series, beginning with the author!) While not technically a space opera, this series does take place in a future populated by aliens and AI superminds that interact in strange and surprising ways with the all-too-human humans! It's a laugh-out-loud funny series that bring a welcome optimistic flavor to what is often envisioned as the dark and doomed future of humanity.