Old Man's War series by John Scalzi. It is at base a 3 book series about humanity a few centuries from now where our species has colonized a number of worlds and is in deadly combat with many alien races. There is a 4th book which is a retelling of the events of the 3rd book from another character's perspective ala Ender's Game/Ender's Shadow and is also worth a read. Like many futuristic settings it could easily be called science fiction but could reasonably be called space opera too. It isn't nearly as space opera as Star Trek but isn't nearly as science fiction as Heinlein - it feels like a nice medium between the two. Of course it has better writing and creativity than Star Trek and better characters than Heinlein's novels which is why I don't hesitate to recommend it if you have an interest in the genre.
The trouble with the series like many others in the space opera genre is that it relies on humans fighting aliens with rifles. That doesn't ruin the experience thankfully but it does mean that it is hard to imagine the real world ever working out even remotely like the series does. Even ignoring nuclear weapons entirely a modern army could wipe out an army of a million soldiers from 100 years ago without taking losses or breaking a sweat. Not only is this true but innovations are not flat year by year but rather are accelerating rapidly. If we were to somehow be colonizing planets and cruising around the stars some time from now and we encountered another species the chance that our two civilizations would have even remotely comparable technology is laughable. It would be nearly certain that they had somewhere between 1 million and 5 billion years of progress on us and as such could presumably annihilate us with the tiniest bit of effort. For our technologies to be comparable they would have to be remarkably similar to us in terms of development, probably within a few decades. The chance of that given that the universe is a solid 14 billion years old is remote at best.
If we continue to assume that colonization and travel through space is a reasonable proposition (which it emphatically is not at the moment) then we must assume that when we encounter some other intelligent race out there it almost certainly will be with a vast power gulf between us. We are likely to either be facing people with effectively no technology at all who are stuck on their own planet or beings wielding technology that is so advanced it is indistinguishable from magic to us primitives. Neither of these scenarios provides much fodder for great space opera though both would be very interesting as far as science fiction goes. Space opera isn't very entertaining when we carpet bomb primitive species nor does it have much to say about us begging for tech from beings of godlike power. It works when there are lots of species of variable forms with remarkably comparable technological progress who shoot each other up in flashy space battles and particularly well when attractive human 'space marines' pick up rifles and shoot at ugly bugs who want to eat their brains.
We aren't getting into space soon, if ever. If we want to colonize someplace due to population pressure we would be far better off to colonize Antarctica than a foreign planet and no one is even considering *that* as a solution. Spaceship Earth is our one and only home and the only place we are going to be shooting up aliens with rifles is in popular entertainment.