HMM I feel like I played this too early...but maybe I also played it as intended? (Playing through this I feel like I got SIGNIFICANT spoilers for Quaint, but now I'm quite interested to see where it's going...)
First, I'll cover the technical aspects again - I really love the celestial themed GUI, as it does fit the "parallel universes" theme. The background is quite nice, and I particularly like the sunlight filtering in from the side (both in the background and for the title screen) - as it gives a v "melancholic sunset" vibe to the atmosphere. Q's slightly different design here is so interesting - one where he's free from the Organization, and has a much looser manner of dress. He's similar but different at the same time, with the same smile and subdued mannerisms but lacking the severe self-confidence issues that he has in Quaint. I like how his differences are highlighted in his design and his mannerisms, and even the coffee shop is different - presenting a universe very similar to Quaint's, but ultimately different.
========SPOILERS FOR TXXX and MINOR SPOILERS FOR QUAINT BELOW=====
While I knew that T was probably still alive despite his "death" in Quaint (considering that the game has two romantic routes overall, I believe), I wasn't quite sure WHERE he was for 6 years. I'll need the confirmation in the game, of course, but I suppose that T was somehow whisked away to this alternate dimension - one where he meets another version of Q (and, I suppose - takes over June's role at the coffee shop?). I do find it interesting that, in this alternate timeline, free from the Organization's thumb, T feels free to pursue a relationship with Q.
This game fleshes out T's character in quite interesting ways. In some ways, he's very selfish, just as he is in Quaint's flashback sequences - he enters this relationship with this universe's Q, well-aware that he'll inevitably have to leave - not caring enough about the effect that his departure will have on TXXX's Q. But at the same time, he demonstrates growth and maturity, choosing to leave this reality despite how happy and comfortable he is here, and choosing to go back to a reality with the bloodthirsty Organization - all because of his sense of responsibility towards his original Q. It's a good sign of growth for his character, although TXXX's Q ends up being a casualty in the process. The game as a whole is sweetly melancholic, with poignant discussions of the characters' feelings, and the "lovers in parallel universes" theme was an interesting one that fit well into Quaint's universe.
(I assume that T's departure at the end of this game announces his reentry into the main game, but I can't be sure! I'm quite excited to see.)
(and as for the title, TXXX...I'm guessing T's real name has 4 letters, and in this game he's struggling with his identity/sense of self - hence why the other letters are Xed out?)
Overall, a very intriguing entry that fleshed out T quite a bit and served as a good teaser for what was to come in Quaint!