Wall of text ahead (I didn't realize I typed this much, lol)
I didn't like the twist that Sean was a robot and not someone with a mask. Yes, the guy in the mask has been used before in VLR, but I still think it would be better if it was someone there. The speculation about who was under that mask was insane. I guess that is the point, to throw us off. Everyone was expecting someone to be under the mask, but... no one was.
That said, I really liked the "Q is actually someone else other than the kid" plot twist, alongside him being Delta, Brother, and Zero. It works similarly, in that everyone thought Zero would be one of the 9 characters, so the twist would be that he isn't, but I think it works here better, and the reason is, imo, Uchikoshi's narrative decisions and the integration of the player-character.
When ZTD got first announced, no one really liked the cinematic approach. We're all in the "we'll take what we can get, since this game almost didn't happen" train. The more visual novel style of narrative 999 and VLR had worked fine, and you shouldn't change something in the winning team. But in Uchikoshi I trusted, and I think it worked.
In 999, there was a reason the game was in first person and had that narrative style. It was meant to put you into Junpei's head as Akane, all built for that twist that she was in the bottom screen all along, seeing the world through Junpei's eyes through the morphogenetic field.
In VLR, there was again a reason for the game to be in first person: the twist that you're actually old.
In ZTD... there really wasn't. And he used that to subvert our expectations.
The whole fragment mechanic, alongside the memory wipes. It is built in a way that none of the characters ever know what is happening, but you, the player, does, all the time. Because you're seeing it all from a different perspective.
The Zero=Delta works, because Delta is a stand-in for the player. His esper powers are perfect, because they're exactly what the player can do: mind-hack, know everything about every timeline by hacking the mind of those that were on those timelines; and, for a short period of time, control someone to make a decision.
So when Delta gets off the wheelchair, he does so in a first person perspective to help that twist. Zero isn't really simply "Delta", a "random character", "someone that we didn't know before". Zero is you. You were manipulating this whole situation to begin with, toying with it as you saw fit. That to me is the biggest mindblown of the game, how it all connected just for this, and that it's left up for interpretation.
Shame he apparently dropped the "?" storyline from VLR, but I think this one worked just fine.
