To kick things off, the reveal of the 4th "enigma" gender (literally on the first page, along with the rest of the omegaverse explanations) killed any kind of tension. With that, when a certain character pops up, it's all but blared, "HE IS IT, HE'S THE ENIGMA". Which is so cheesy—because what can we do to spice up omegaverse? Add a 4th secondary gender, of course!
Strangely, there's too much plot—even if most of it isn't that interesting. Scenes change abruptly, the side characters are poorly established (I still don't know who some of them are, whose side they're on, or why), and there's the occasional interruption for the obligatory sex scenes because it's a BL. In fact, you could skip to only the scenes with both Tsukasa and Tougo, because they summarize what the side characters are saying.
On that note: it's teeming with yaoi clichés. The whole "I'm raping you because I've been hired to, but I also love you". The withholding information on purpose Because Plot. The "brothers fighting over the family business" subplot that holds zero tension. Oh—and Tsukasa instantly becomes a weak damsel after turning into an omega, which is just boring.
There are some interesting bits of plot hidden in there, but not enough to justify going through everything else. Here, if you want to know the interesting bit:
The orphanage Tsukasa was raised in was a front for experiments on children to create the "ultimate alpha". His adoptive father was an investor there, but that's OK, because Tsukasa was conceived between him and a woman out of love—not like the other test tube babies! Tsukasa is given a vaccine that somehow makes him forget all of this; years later, he's turned into an omega by Tougo (who is the famed Enigma), becomes his mate, and they all live happily ever after.
I'd also like to point out that, at the end of it, we still don't know what an "enigma" or "ultimate alpha" are. He's so much of an enigma, that not even the author knows what's with him!