This started off as a mixed bag, and around the halfway mark it got worse.
I think that this started off as something really special. I don't mean the first few chapters—they're fine, I guess—but the creator's vision for the series as a whole. The core plot of betrayal and revenge and regret obviously came first, and when that's the focus of the action, everything is good—the characterization, the plotting, even the art. (More on why in a minute.) But the creator also added all this political intrigue, which is at best okay, and a larger plot that is the focus of the last third or so, which stinks. And the ending (a) came out of left field, (b) didn't include any of the character-arc payoff we were expecting, and (c) was incredibly rushed. I think that by the last volume of the series, the creator must've been as sick of this story as I was.
That brings me to the characterization. Again, when the focus is that core narrative of betrayal and revenge, it's pretty solid. The villains are a bit too villainous—and it's never explained how they can get away with being so nakedly corrupt when the emperor is (eventually) portrayed as being wise, perceptive, and active—but it's not awful. But as soon as we get away from the betrayal/revenge narrative, and particularly as the revenge plot fades into the background and the Big Bad's evil scheme takes over, that changes. The villains get dumber and more blatantly evil. Everyone starts holding the Idiot Ball at once. People change their allegiance without adequate explanation. Ichfeis goes from being a cold-blooded opportunist to the biggest, dumbest idealist in the series.
But what really sinks this series, IMO, is the art. For the most part it's competently executed, but there are some pretty bad panels that seem to show a difficulty with perspective. And for a manga that focuses so much on swordplay, there's basically no effort at depicting the swordplay itself, and no variety whatsoever to how the fights get resolved. They almost invariably go like this: (1) a few panels of sword clanging on sword, (2) Koinzell (or whichever good guy is fighting) gets a cut diagonally across his left shoulder, which never so much as inconveniences him, and (3) Koinzell ends the fight using one of his two magic sword moves. At that point, either the enemy is dead (yay, hero wins!) or the enemy is still standing, in which case Koinzell collapses and is saved by the intervention of some other character.
All of that got the art down to about a 6. But I docked another two points for some really egregious pedo fanservice. There are a lot of naked women in this manga, and there's a fair bit of sex. Fine. Whatever. Not my thing, but I won't complain about it. But there is a young girl whose sole reason for existing, as far as I can tell, is to appeal to perverts. Her combat attire would make perfect sense as lingerie. At one point she forges a sword wearing heavy protective gloves and a bikini bottom. Absolutely ridiculous. Another young girl wears an armored thong into battle. This doesn't just offend my sensibilities. It also makes it impossible to take Ubel Blatt seriously. (By the way, this is what I meant when I said the art is better in the revenge-focused bits: The revenge story doesn't involve any young girls, so the author doesn't have any opportunities to put lolicon smut in those bits.)
Bottom line: Not hopelessly incompetent, and even had some good points, but overall a big disappointment.