*It's a really entertaining series. I typically buy e-books to read while on the elliptical at the gym (my hour and change goes a lot faster when there's something I can look at besides the timer) and this is something that makes my cardio routine go by in a flash. It also makes the MARTA train when I'm going to graduate school much less boring. Even on re-read #3 for both books, things go a lot faster.
*The aliens when they're finally revealed are the most interesting extraterrestrials since the "fish" of Midshipman's Hope and its sequels or the alien-invasion novel Footfall. Most fictional aliens are human-sized or, like the Fithp of Footfall, slightly larger. The Lankies somewhat resemble the Baluchitherium of prehistoric Earth--but are vastly bigger.
*As the protagonist himself points out, the idea that the warring factions of humanity would unite in the face of a common alien foe is pretty cliched--and does not happen. The North American Commonwealth and the Sino-Russian Alliance continue their war even with the wolf at the door. Although cliches can be plausible, it's generally good to avoid them.
*It does touch on the less-romantic realities of space colonization--going from an urbanized Earth to some new colony where there are maybe a million people on an entire planet is going to be pretty jarring and lonely.
*Kloos started out as a self-published writer using the Kindle Direct Program and then 47 North, Amazon's science fiction imprint, picked up him. He's a success story those of us who seek to walk this path (I'm still primarily interested in the traditional route, but I could easily imagine going down his path if I keep querying and nobody bites) could learn from.
*The male lead and female lead are in a romantic relationship lasting for years, but she's an officer and he's senior enlisted. That's a serious no-no right there. Kloos is a veteran of the German military, so he should know how these things work. Some acknowledgement of the situation would be a good idea--it could be pointed out in-story they're not in the same chain of command (that's probably the case) or due to long space voyages the rules aren't as strictly enforced.
*We're getting into spoilery territory here, but in the second book it's made clear that there haven't been any human victories in space over the aliens. A solution is ultimately found to that problem, a solution that's pretty simple and obvious. Given how dumb people can be sometimes and how the NAC government was covering up just how bad things were, the fact that this solution wasn't thought up immediately isn't the implausible part--what's implausible is that in-story it took five years. If the war with the Lankies had only been in progress for a year or two that would make more sense, plus it would make the Lankies a lot scarier if they've obliterated half the NAC's space colonies in that sort of a time-frame. It would also explain why the NAC and SRA haven't ended their chronic war--five years is quite a long time to keep fighting in the middle of a burning house. Kloos has written a response to this issue (warning: spoilers) here if anybody's interested.
*From the way they talk about the use of nuclear weapons (and the strategies the humans follow against the Lankies), it seems Kloos thinks the use of a few nukes on a planet would render it uninhabitable to both the humans and Lankies. Unless they're using cobalt-salted bombs, that's not plausible. Hiroshima and Nagasaki were immediately rebuilt and re-inhabited after they got A-Bombed. To be fair if he was a German soldier during the Cold War even tactical nuclear use in an area as densely populated as Germany would be horrifically destructive, but whole worlds are not single countries.
*The Earth is rapidly overpopulating and it seems most of the urban population in the NAC is living on welfare. Some more discussion about how this situation actually came to be would be interesting. If it were me writing it, I'd say that the economy is so advanced that it can generate all sorts of high-tech goodies but automated to the point it only creates a few jobs. However, the government is so starved of funds (due to overly-low or misdirected taxes, an inept tax-collection apparatus, or some combination of the two) that it can't manage guns and butter (and so the masses are reduced to living on soy in crime-ridden ghettos), that its needs are so great it's debasing the currency to meet them (and that's why beef is $100/pound), or a combination of the two. Kloos obviously shouldn't have to explain everything, but at the same time, the reader shouldn't have to come up with explanations for why something works to this degree.
A good series despite some world-building flaws. Definitely worth keeping up with. 8.5 out of 10.