One bit that feels unsatisfying is the complete underreaction to Harry's "oh btw Voldemort's alive, here, I brought him with me."

So instead I Obliviated most of his memories, then Transfigured him into this." Harry raised his hand, and silently pointed to the emerald on his ring.

Splat. Boing. Splat. Splat.

"Huh," Moody said, leaning back in his chair. "Minerva and I will be putting some alarms and enchantments on that ring of yours, son, if you don't mind.

I immediately thought of a scene in the Eye of the World:

It was his sword she touched, not him, her hand closing around the hilt at the very top. Her fingers tightened and her eyes opened wide with surprise. “A shepherd from the Two Rivers,” she said softly, a whisper meant to be heard by all, “with a heron-mark sword.”

Those last few words acted on the chamber as if she had announced the Dark One. Leather and metal creaked behind Rand, boots scuffling on the marble tiles. From the corner of his eye he could see Tallanvor and another of the guardsmen backing away from him to gain room, hands on their swords, prepared to draw and, from their faces, prepared to die. In two quick strides Gareth Bryne was at the front of the dais, between Rand and the Queen. Even Gawyn put himself in front of Elayne, a worried look on his face and a hand on his dagger. Elayne herself looked at him as if she were seeing him for the first time. Morgase did not change expression, but her hands tightened on the gilded arms of her throne.

While that would be an over-reaction in the HPMoR scene, at least there should be, well, some reaction to discovering that Harry is wearing the biggest threat of their time on his finger.

So, QQ was Ravenclaw and David Munroe was Slytherin (?)... Both facts are public record. Yet QQ is celebrated as "the best Slytherin that ever was".

Someone is bound to ask questions.

He wouldn't have had enough information to conclude that Harry had invented a new type of Transfiguration - he would probably think it was a particularly powerful cutting hex for a first year, or something. Still stupid of him not to have made inquiries after two times witnessing its effects (cutting through the wall of Azkaban, felling the trees).

Shouldn't Harry have fallen to his knees twenty seconds earlier, if he originally heard/saw the explosion via Voldie-simulcast?

I feel like the problem turned out to be unnecessarily easier than it had to, that too much of the credit is due to luck, and some things could've been done better (Death Eaters could be saved). It's somewhat of a theme with all these spells and rituals being performed in unique situations and working on the first try, with little precaution taken to test them or theoretical grounds to expect reliability. For example, Hermione still wasn't tested. It's the first resurrection ever performed, at least by the people present. It involved further effects that might've never been combined in this way before. The person who knows the details is now defunct. He didn't plan to test it either, for the primary use case intended. Hermione's brain is warm and might be losing information or she might get terminally sick soon, with brain damage. We just assume everything worked.

One problem is that Harry didn't know that he can remain conscious after directly casting a spell at Voldemort, so it should've been planned around, with the less direct transfiguration being plan A for rendering Voldemort unconscious. We now know that this might've failed (more likely than before Ch. 114), and there had to be another attempt. But failing to remain conscious while Voldemort is unconscious amounts to losing the war, so it was very important to avoid risking that Stuporfy. For example, grabbing the Time Turner might've been a better idea, then he could've made the same shot at the same time using the future self, but with an ally ready to Innervate the future self afterwards and/or contain the resulting unconscious Voldemort. Voldemort, in turn, should've made more of an attempt to get out of there in response to the situation he didn't understand, rather than just dodging. Then there's the wand, which had no place being available at that particular moment. It should've been used around when the Vow was made instead.

The setting also made it possible for Harry to cast further spells on Voldemort, even Transfigure him. This capability isn't necessary for the tasks at hand, as he could've got help. In any case, Transfiguring Voldemort into an inanimate form wasn't a safe thing to do (at least he didn't apply the Stone, which might've made it a regular ring unrelated to the original body and unable to anchor the spirit, although it might eliminate the spirit if it was also Transfigured). It might've let the spirit free (either by default or as a result of Voldemort preparing for this possibility), so at least there should've been further precautions taken before (such as making a Harry-Transfigured sarcophagus around the body to attempt containing the spirit). Further precautions unknown to Harry could've been taken by using the Time Turner to summon help to arrive immediately (not to mention saving the Death Eaters by cooling their brains, so that after all nobody had to die). Harry continuing to blast the body with resonance stunners could've prolonged Voldemort's unconscious state. Drugging the body would be further redundancy. If a Transfiguration of the body is risked, it could've been into a living thing, paralyzed-by-construction and with a smaller brain.

Severely Obliviating Voldemort wasn't a safe thing to do, as having an insane immortal spirit might be a very bad thing in the long run (such as in a thousand years, assuming no intelligence explosion), if it ever got out of the body, for example as a result of the body getting Transfigured. We know Voldemort doesn't want the World destroyed and is at least somewhat human, but a person resulting from centuries worth of reflection by an insane remnant of Voldemort might want some very strange things far removed from human values. Torturing to insanity would've been even more irresponsible. It was better to avoid these events, if possible, and at least delay them until further consideration if Transfiguration was planned as a method of indefinite temporary containment. For example, a more careful Obliviation by a more experienced wizard could've shaped the person to have more agreeable values and less capability (and could be applied immediately, via Time Turner, to avoid Transfiguration). If the result is no person at all, there should be an understanding of the process that guarantees that after a million years there still won't be a person in the spirit.

Dumbledore gave Harry a pack of cards that had portkey functionality, under the name Santa Claus and claiming that they were a portkey to Salem, but instead heading to a location somewhere in London. Harry gave them back for further investigation, thinking that they might be a trap, Dumbledore took them back but didn't activate the portkey.

It's possible that this was just a short reference, meant to establish Dumbledore's steps of trust in parallel to the gift of the Cloak of Invisibility, and that Harry did not retrieve the portkey and Dumbledore did not place it upon Harry's person...

But activation trigger was to rip the King of Hearts -- a king card known for its face character stabbing itself in the back of the head -- in half.

Harry could start by saying "Not sssure if I should ssspeak. Mussst asssk friend firssst." He will won at least fime, at best an ally.