All three stars are for the narrative device/formatting. It is simply the most interesting means of telling a story I think I have ever seen in a YA novel, and it works brilliantly. Illuminae is presented as a dossier of hacked files compiled by something called "The Illuminae Group" (about which we know nothing) for someone with the title of "Executive Director" (of what, we don't know). To what end? You'll have to read it to find out! 
 Illuminae presents a worldview in which corporate greed is the great evil, but the military hierarchy can't be trusted either, and it's up to the subversive hackers to save the day and ensure that the truth gets out. I think this appeals to a lot of readers, but I found the presentation of the big ideas to be a little lacking in finesse. I do see potential for the series to grow in this regard, however. 
 But the main reason I personally didn't really like Illuminae was that I found the story itself so incredibly terrifying (and not quite interesting enough on its own to justify the terror). It starts with the destruction of a colony planet, and just gets worse from there in a high-tension series of events that frankly made me feel panicky. I guess that any strong emotional response is a credit to the writing, but given that I read YA for "lighter" reading, I found it to be really unpleasant. Note that if you go for this sort of thing, you will probably totally love this book. I think I could have put up with it a little better if I had found the two teen protagonists and their relationship to be particularly interesting, but they were kind of just serviceable for me.