The first season of "No Game No Life" had one significant flaw: it didn't really have a proper ending, only hinting at characters and arcs that would appear in seasons never to be. That made "No Game No Life - Zero" an odd choice for studio Madhouse to agree to: it's a prequel, so it wouldn't really satisfy fans, and would only spur more rumors that that staff were prepping a season two. And yet, the feature film prequel came to be. Sequel films to a film or television series can be trickly to formulate. With "No Game No Life - Zero," they took the Disney approach, by which I mean the "sequel-films-animated-by-Disney's-television-teams-and-released-straight-to-home-video" plan. If you grew up in the 1990's when VHS was readily available for home use, you are probably familiar with the sequels to "Aladdin," "Peter Pan," "Beauty and the Beast," "Lion King," "The Little Mermaid" and several others. Those films sometimes had a brand new story actually worth telling, but often were simply two or three television series episodes tied together with segments of current-time characters reminiscing about the good times they had. "No Game No Life - Zero" also does this, with bookended (and a middle bit) clips of the God of games Tet retelling the story of the land from many generations past. It's a shame, since had they removed this, the film might have been better suited to viewers not familiar with the original show, although for fans of the show desperate to see these characters again, this might be all they get.Anyway, yes, the film features a completely new cast of characters from a very long time ago in the land of Disboard. Aside from the unnecessary references to the main show, the film immediately shows off that this is a proper film and not just a cash-grab. After an impressive tracking shot through a desolete canyon with white ash falling from the sky, we see a small team of humans scavenging through old factories and metalic pipes. We learn the ash is poisonous. We see a large monster discover the humans, and the leader coldly tells one of the men to sacrifice himself for the rest to escape. When getting back to the underground camp, a young girl asks why her father is not with them, and the leader, Riku, quietly retires to his room, where he yells and screams at the ground for the fate they are forced to live. This is simply the world humans live in: playing games to resolve conflict isn't a thing, and instead other species rely solely on their might and destructive power to wipe out other races and expand their kingdoms. In a world of angels, robots and demi-gods, humans are at a meek disadvantage, and struggle to keep their group alive. It isn't until Riku happens to stumble across an abandoned robot named Shuvi, with a vareity of helpful abilities not previously available to the humans, that their luck starts to turn around, as Riku hatches a risk-all strategy to turn the other races against each other while prepping the humans to take control of the land and rewrite the rules for themselves. While a bit of comedy is still present, this is a significantly darker and bleaker world then the Disboard we were familiar with in the television anime. And for a film, it is all the better for it. "No Game No Life - Zero" does come to a proper ending, and it has more emotional heft than most other anime due to its subject matter. Perhaps a bit too much emotion... many of the main characters will explode in tears, banging their fists on the ground at their situations, quite often and with less subtlety than I've seen elsewhere, but given the world they live in, I understand. The grand scheme that begins their path to take back the world doesn't necessarily sound all that exciting either if you write it down on paper, and the conclusion to the plan can require a rewatch to fully understand, but the direction and acting help make it feel more significant. And it's a tragic tale too, a fair warning, not all characters will make it to the ending alive or in one piece. 
Despite any flaws in the story's outline, I can't recall an anime that felt this powerful or emotional. It cranks the "feels" up to 11. Because of that, it is easy to exclaim that "No Game No Life - Zero" is better than the original show, a rare feat for any sequel or prequel. And the only real improvements came in the story department, and in the improved theatrical quality animation.Aside from the powerful story, is there anything fans of the show can get out of this? You get small snipets of present-day characters, and a handful of immortal characters from the show appear in the film's main storyline. The most noticeable takeaway is that several new characters look or act like doppelgangers of characters from the show. The most obvious is how Riku and Shuvi look like mirror images of Sora and Shiro, enough so that fans were confused when the first posters for the film (without much hints to the story) were revealed. The writing has a bit of fun with this, letting us know they understand the comparison and fullfilling things that couldn't have happened in the main series. For example, Riku and Shuvi get married by the mid-point, an emotional moment in its own right, and especially so given that Sora and Shiro are siblings in the present day (they wouldn't marry even if they were certain they wanted to). Either for comedy or to enhance the importance of a relationship, these moments brough a smile to my face as a fan.While "No Game No Life - Zero" is defintely appreciated best by fans of the franchise, even newcomers can appreciate what is accomplished here. It's hard to imagine a franchise film turning out better than this.