This VN was...something, and not in a good way.
Here are some of the most notable things about this VN (Spoilers, obviously):
Overall, the plot was very predictable due to the authors' reliance on the technique of the Chekhov's Gun. For instance, when Alexios and Cassius won the first trial, someone analyzing the VN could predict that Amicus and the MC were going to win the second trial despite the video showing Amicus having sex with Neferu. Why? Because the audience is told that there are three trials, so of course the plot is going to be set up in such a way that the third trial comes into play. More on that later. I know that tropes are tools and all that, but this particular trope is VERY overused in this VN. Though it does make for a fun exercise in predicting the plot as is fitting of a TVTroper, the plot itself is not enjoyable because of it.
Speaking of that, it didn't really come as a surprise that Cassius got dirt on Amicus as, of course, we see him sneaking around in Amicus's quarters. On one hand, this and other instances of foreshadowing in the VN do provide a justification for certain events occuring, rather than making it seem like an ass-pull. On the other hand, the sheer amount of Chekhov's Guns in the story makes it incredibly predictable.
I've criticized another VN, called Far Beyond the World, for having characters act dumb for the sake of plot, and this criticism applies to Adastra as well. For instance, when the MC and Amicus land on Adastra, the MC says that he would like Amicus to put away the Nervo (The space taser thing) because he "Doesn't want to think about it", something which comes back to bite him in the ass later on. Why the hell would ANYONE want to discard their one hope of being somewhat on par with an alien being on a planet god knows how far away from home? (Though, to be fair, even if the MC didn't throw away his nervo, Cato and Cassius still would have overpowered him in that scene)
And, of course, Amicus and the MC suspect nothing whatsoever when they see Cassius sneaking around their quarters.
There's also the fact that Virginia and co. try to get Cassius to abdicate the throne in front of a known spy. Of course, things go south after that.
Then there's the plot contrivances. It seems as though the authors first decided on the plot and then had to figure out how to have the setting fit into it. There's the obvious case of the triumvirates declaring Amicus the victor in the second trial. This is handwaved as "Oh, the triumvirates are corrupt AF and Cassius said that he wants to get rid of them, so they voted against him". No matter how it's explained, it's a glaringly obvious plot contrivance that came into play for reasons discussed in the first paragraph. It's awfully convenient that they didn't decide to vote against Cassius in the first trial, though.
And, of course, it's VERY convenient that the cameras around the palace don't actually save recordings of events, or that anyone can access the records willy-nilly, or that the security drones can't aim when Cato orders the computer to kill the MC.
The part with the MC surviving his avia pox infection is not only a clear plot contrivance, but reeks of another trope. Yes, I know he is supposed to be chosen by the Parents to advance their goals for the Siblings, BUT the fact that the plot of the story just went "And so the MC survived his outbreak of what was supposed to be a fatal disease completely fine" is yet another plot contrivance. However, even if we disregard Marco's survival on the basis of avia pox being a fictional disease, and so maybe that's just how it progresses, the part about his presence on Adastra being the will of the Parents as part of their goals for the Siblings makes for yet another trope: the trope of the Chosen One. In my opinion, the trope of the Chosen One instantly makes a work orders of magnitude worse than it already is. The character is never in any peril because he was chosen by a divine force to carry out a certain plan (Honestly, I like the version of events where the MC dies better. It's a good subversion to the usual trope of "The main character is never in any actual danger when put into a dangerous situation". Alas, that's not the canon sequence of events.).
Not only is the MC of Adastra a Chosen One, but, in the complete series of events, he is saved by yet another plot contrivance that was the result of yet another Chekhov's Gun firing. Boooooooooo.
The one thing I liked about this VN (Besides it being a good study of certain tropes) is the way Neferu is written. He gives off "magnificent bastard" vibes, and I would say that scenes involving him were generally very enjoyable to read.
Oh, and the scene where Amicus introduces himself...since I know that Amicus means "friend" in Latin, that made me both chuckle and cringe at the same time.
Overall, I would say that this is the second-worst VN that I've read, only behind FBtW, but I'm going to future-proof this in case another VN comes along and knocks down Adastra to number 3 on my "Worst VNs I've read" list and simply say that this has been one of the worst VNs that I've read. Most of it, with the exceptions discussed above, is about as enjoyable as watching paint dry. There's probably lots of things I haven't touched on, but this was a very forgettable VN, and I definitely don't feel like replaying it. Those are hours of my life that I'll never get back.
TL;DR: If this is largely considered a good VN, then I'm VERY terrified of what people consider to be a bad VN.