I did not think card games and raves worked together, but I was mistaken.
I value two things most of all - story and style. In the genre of TCG tie-in anime, there isn't a lot that can be done with the former. At the end of the day, tabletop gaming is a constraining plot structure. The simple solution, which Zenonzard has realised immediately, is to pull out all the stops on the latter.
Not just the the field of play, but the audience, the stage, every single aspect that can have been brought over the top, has. The cast is colourful both in and out of the game, the UIs are nicely modern and surprisingly legible, and even near-emotionless AI can give a ton of personality just through their excellent designs. It's literally astounding.
While the plot is nothing new, an absurdly popular card game exists that the protagonist plays, said protagonist does have a bit of interest behind him. Unlike other TCG characters, he does not initially want to play the eponymous game, despite his latent interest and history with it. It's a decent idea that I hope could be expanded upon in the full series.
There were elements of an overarching subplot in the opening scene, but this does not get brought back within the duration of this prologue, though appear to be important in the sequel. I wouldn't say this scene helped as there is no conclusion to it, and may have been better suited for the rest of the show. The only annoyance really is that the rules of the card game are not explained other than a few brief comments of a side character, but I'm willing to let this be assuming explanations are done in the main series.
The art is, as stated, excellent. Even outside the game, the characters look really good, even the normal, mostly realistic designs of the students. The animation does wane a bit with the use of CGI, which can be very detrimental to some viewers but I thought worked well enough. The editing and direction are mostly normal but have standout moments with very impressive angles and shot setups, particularly during the climactic card game.
The music is exceptional, and while used sparingly in the first half pays off tenfold in the second and the ED. The entire game is almost fully scored and synced with the music, and it really helps build excitement during each card play.
The tone and design of the world itself is interesting, and has a lot of nice elements. The character designs fit in when necessary but are also able to be distinct enough, with each Codeman having a distinct palette and motif. Even background characters from The Zenon, each barely seen, have multiple interesting elements in their appearance.
Needless to say, Episode 0 has sold me on Zenonzard. I can't think of much that I think would improve it other than fully explaining the rules of the card game. Nevertheless, if the main series can keep the same flair and energy, I will certainly be invested.