What SM said.
Also, it's not packed with technological alien life. In fact, that's rare, the only ones we keep encountering a lot are the Predators, and that's only because the gits keep coming to hunt us. Everything else is so far away that it's economically implausible to keep contacts with them. Literally, everyone's on their own.
Even our very first encountered alien race, the Arcturians, are so distant and silent to us. The human settlers on Arcturus have been isolated there for long enough to start developing their own racial traits, you could tell an Arcturian human just as easily as you could tell a member of a different race such as an Asian or an African etc. No Arcturians or humans from that system appear, this is just mentioned by a human reporter who encountered some human Arcturians.
It still feels like Alien at times. Space travel is still difficult and takes a long time to get to places. The universe still seems to be callously trying to murder us in many ways or break our minds as we try to take shortcuts through wormholes. Lebbon truly respects the scale and dangers of outer space and our inability to adapt to it.
Aliens are by no means placed to the side, I don't know why it seemed that way. They were the most dangerous Xenomorphs I have ever seen personally. Right from the first book I gained a ton more respect for the Alien monster. And by the third book, I see exactly why Weyland-Yutani keep busting their arses trying to weaponize the bloody things lol.
Spoiler
The Dog-Alien ruins are still mysterious and it makes you question their fate a bit. Things seem different compared to their colony on LV-178 and this artificial world of Midsummer.
Just who are those creators of the Faze, biomechanical slug things that build and improve upon existing technology but with a mysterious agenda? Are they even sentient or simply tools left behind by long gone creators?
Overall, it's really refreshing. It's not the usual "Predator hunt" or "Alien infests ship/colony" story. It has elements of those two, but it delves into a much grander picture. Aliens infest en masse, controlled by a very human enemy using ancient leftovers from a mysterious civilization to control them. The alliance with the Predators was the most natural alliance I have seen that could possibly happen with them.
It was filled with distrust, filled with tension that the two allies could turn on each other at any moment. There's no patting each other's backs, not even
Spoiler
at the end lol. They pissed off with all the leftover alien tech, leaving us 500 years back now that all our dropholes are gone and we're pretty much back to Alien era ship travel.