First, the bad. Harry is not a nice person. I don't mean this the way he means it, which is that he is dangerous to be around and is totally ok lying and messing with the law if that's what it takes to get his way. I mean how he is manipulative.
Consider in the first chapter: "All he had to do was convince Sev to love him again." Now, I don't know quite what brought the two of them together in the Mirror timeline (or rather, why they stayed together, anyway), but in this timeline, Harry has has already made his choice. He know he wants Sev. And he knows that Sev would not want him as he is. He wants to make Sev love him. He wants to coerce Sev. Even the word "convince" suggests that he's not going to take no for an answer, that he's going to try and try again. We're already into seriously creepy territory here.
But Harry is totally OK with using anyone as his pawn. Remember Filch? In the Mirror, he and Filch slowly developed respect for each other. But:
"this time around Harry simply didn't have time to play "Hi, let's be friends". He was also pretty sure that such an approach wouldn't work on the sour mistrustful man.
So instead of a pleasant introduction followed by the tentative "getting-to-know-you" phase, Harry was going to go straight to shock-tactics and bribery. Then, once he had the man's attention, he would set himself up as both teacher and mentor. That would hopefully create the feelings of trust and commitment he needed."
Really, Harry? Shock tactics and bribery? With that sort of thing you'll get him to be terrified of you--not that hard, given that you're a War Mage already-- but you'll never, ever get him to respect you. How do you possibly expect that someone who you're planning on shocking and bribing will ever accept you as a teacher and mentor?
What about his deal with Gringotts? He walked into Gringotts and said, "You have a big potential security breach, and I'm the only one who can fix it. So you have to give me access to your secrets AND give me a big pile of money." Why would anyone take his offer seriously?
Now, another big issue with the fic: it's still not finished. Given how long ago the last chapter was posted, most people assume that it will never be finished. But let's think about what has to happen before the fic is done:
-Voldemort has to get super-scary. Harry's already scary enough that he can take out a whole squadron of Death Eaters with his pinkie toe. But he's somehow afraid enough of Voldemort that he needs to recruit Filch, get the Circle involved, and train a whole troop of Muggles. Midnight Blue has already given us a menu of ways Voldemort can get scarier: he's already started to become a Soul Mage, and he's researching both wandless magic and electro-magic. Also, Dragonfire is still a possibility. Now he needs to get good enough at any of them-- perhaps all of them-- to make the fight worthwhile. She needs to prove to us exactly why Soul Magic is so scary. Or she can give him Robert Thomas's secret. (Or both.)
-It needs to develop into an all-out fight-- maybe not one that the Ministry recognizes, but a battle nonetheless. For proper dramatic tension, Harry's troop of Muggles cannot be fully trained by then. Or they can be fully trained in all the wrong things. And Voldemort needs to have developed at least one super-weapon before it happens.
-We need to see the Foundation Stones of Gringotts again. She said in Chapter 2 that they became an invaluable tool for the forces of Light-- the fic will not be balanced until we see them come into play again.
-Harry has to reveal his identity to Sev, and possibly to Ron and Hermione as well. He's been in hiding for most of the fic, but it started with him as Harry, so it has to end with him as Harry.
-There has to be some sort of fallout with Sev. I don't think Sev will particularly mind that War Mage Ash is really Harry, but he is definitely going to mind all of the lying, scheming, and manipulating that Harry has done. Like telling Draco to ask Voldemort to ask Sev to sleep with Harry. That's a pretty big mood-killer in my book. But if there's never fallout from anything, the fic will simply not even be following the way romance stories work.
Midnight Blue wrote an awesome 20 chapters. But I don't think she's proven that she can write another 40 to finish it.
Of course, you could pretend that it's already finished: that the point of the fic was to get Harry and Sev together, albeit under peculiar circumstances, and to set up the fight that everyone knows Harry will win. She's already given us enough information that we can more or less predict what's going to happen in the next stage, as I've outlined above. And if she considers Harry and Sev together, then the romance part is over too. Chapter 99 is just an epilogue. If you're thinking at all like this, you'd be bored and frustrated trying to write more. But I don't quite buy it.
So with these issues, why do I keep coming back to it? There are some pretty awesome fight scenes, like the one with the fake Ked'rallirri-- I get shivers every time I read just the way Harry throws those three knives!-- and I loved the Polyjuice interview. But there are fight scenes as good in countless manga. (I have always been quite sure that Midnight Blue is a huge anime fan.) There are even scenes as delicious as that Polyjuice interview-- Harry giving carefully misleading answers even under the strongest magical truth serum; Harry's pulse racing as Severus takes it-- in countless stories.
And I think what really kills me is the setup itself. You have Harry ripped away from the Hogwarts he loves. You have him dumped back into it-- and he's changed so much he can't really come back. There's this sort of wistful tension that permeates the fic. Remember that line in the first chapter? "Severus...?" No one in the Great Hall then had any idea why Harry was so happy to see Snape (or Dumbledore)-- but we can guess. And I like that second-chance aspect too, that this Harry has the tools and the knowledge to do what he has to do this time around. Harry is sad that, in a sense, he lost his whole world, but happy that he gets another chance to try again. Then add in the cool fight scenes, the political wheelings-and-dealings, the plot dominoes all getting slowly set up, and I'm sold.
I'm definitely going to read it again.