From the art, character design, characters relations to each others, BGM, and the flow of the story : I trully adore it (although the romatic endings seems a bit in rush, but somehow covered with characters background story in Extra).
And how I love the heroine's makeover (if the heroine wasn't stated as female, I would have predicted she will be an androginous or even non-binary character), and she remind me to Jordan Baker in The Great Gatsby xD
Maybe it's just me overanalyzing, but I realized that :
a. the LI's usual work attires are contrary to their own selves (Alexei's red shirt to his calm-collected demeanor + water-based magic, Gio has blue shirt vs his friendliness + "back to Earth" magic, and Emilio with green vest although his fire magic + hotheaded manner); but their New Year's suits, especially the colors of their ties, are compatible with their "true nature" and their magic specializations :D
b. I can't help to notice that golden ring as heroine's POV background is somehow an irony for the Cycle of Revenge Ending, but a great signification to Ring of Promise Ending, and oh I can't forget the CG is pairing the happiest and saddest scene of each routes :')
Last bot not least, the LI's POV when repeating the story and that New Year's Eve "infiltration" to the lab are much appreciated xD