Prequels are hardly an unusual phenomenon in anime in recent years, though most typically they fall into the domain of supplemental OVA episodes included as bonus material on DVD/Blu-Ray or manga releases. (Another and Sankarea are two simulcasting series which have already done so this year.) Thus a full 25-episode TV series serving as the prequel to another series is a rarity, but that and the way that the prequel wholly exceeds the original in virtually every production and storytelling aspect aren't even the most striking details that make Fate/Zero – and in particular its second part – special. That honor instead goes to the series accomplishing the remarkable feat of actually making the original series better.

Yes, the series accomplishes this partly through filling in the details about the past that Fate/stay night either glossed over or entirely skipped explaining, and yes, it does present some scenes which turn certain scenes in F/SN into crushing works of irony, but there's more to it than that. Aside from sheer entertainment value, the most important thing that this series does is to establish a critical context for its predecessor. That the series is actively doing so – or at least the degree to which it is actively doing so – is not readily apparent until the final episode, but the result is undeniable. What happens to Saber over the course of this series provides a much clearer explanation for why she behaves the way she does in F/SN and makes the resolution of her story in F/SN vastly more satisfying, while Shirou Emiya's irritating obsessiveness with being heroic in F/SN suddenly becomes far less grating when looked at as a counterbalance to what his adoptive father Kiritsugu thinks and does in this series; Shirou is, in effect, the embodiment of what Kiritsugu lost in his quest for heroic pragmatism and what he was seeking from the Grail, which makes F/Z's choices for its final scene and line to be particularly powerful and poignant ones for those who have seen F/SN. The progression of Kirei's development over the course of this series also goes a long way towards explaining Kirei's behavior in F/SN and the true Rin/Sakura relationship is laid out much more clearly. As an added bonus, most of the main cast members from F/SN make at least cameo appearances as young children, with Rin even being the exclusive focus of one episode; she was already a fan-favorite character, and that episode will only enhance her status further.

Fate/Zero has a lot going for it even if it is just looked at as a standalone project, though. Its first season (and especially its double-length first episode), which constitutes episodes 1-13, does tend to get bogged down in the needlessly lengthy dialogue blocks that Type/Moon titles are all too well-known for, but by early stages of the second season (which constitutes episodes 14-25) the series has gotten most of that out of its system; beyond episode 15 the problem pops up rarely and is less protracted and cumbersome when it does happen. Even if one can make reasonable assumptions about who's going to survive to be involved in the series' climactic battles, the oft-cruel and sometimes unpredictable twists, turns, and gamesmanship that the series takes to get to that point are great fun to watch. Anime in this vein (including F/SN) so often rely so heavily on hotheaded heroes and background powerbrokers to drive events that watching primary characters like Kiristsugu, Kirei, and Tokiomi (and to a lesser extent others) tactically orchestrate events to achieve certain ends is refreshing. That all but one of the Masters is an adult this time is also a refreshing change of pace, as is the way many of the Servants interact with each other; some of them clearly respect one another and three who have been kings even spend most of one first-season episode sitting down together for drinks while discussing their conflicting philosophies on what it means to be a king.

The character developments and interactions in the series are also enjoyable, especially watching the vastly varying natures of the relationships between Masters and Servants and the way they develop over the series, from the thoroughly disgusting degree to which Ryunosuke and Caster become utterly in sync to the troubled relationship that Lancer has with his Masters to the great, wholesome bond which forms between Waver and Rider. The connection between Kirei and Gilgamesh also takes some interesting developments here as it progresses toward the arrangement that they had in F/SN; Gilgamesh's bemusement with watching Kirei gradually develop into a monster has a certain kind of charm to it, while his growing interest in Saber has a creepier tone. On the other side stand Kiritsugu and the veritable harem of adult women in his life. (Like father, like son, it would seem.) While his mutual love with Irisviel and the ardent devotion of Maiya remain constants, as does the friendship which develops between Irisviel and Saber, friction eventually grows with Saber over their vastly differing approaches to the same basic ideology and Maiya and Irisviel eventually come to a certain understanding about the man that they both love. Kiritsugu's mindset is also important enough to the way events unfold that the series devotes two entire late episodes to a flashback which firmly establishes his background and how he came to the viewpoints that he now has; while this may seem an annoying distraction when it starts, by the end of the flashback the reasons why it had to be told, and told at that point in the story, should become clear. On the weak side, Kariya is such a put-upon character that any sympathy he might engender gets driven into the ground and Berserker gets short shrift when his true identity is finally revealed in episode 23. There are some indications that episode 24, which should have elaborated on it, was trimmed to fit into the TV broadcast time window, so this could get fleshed out a bit more in the series' upcoming Blu-Ray release.

For everything else that the series does well, its real stars are its elaborate action scenes. The few first half has few of them, but one of the earliest ones, which eventually involves five of the Servants, is such a thrilling spectacle that the series has to work hard to equal it again. An aerial duel between Berserker and Archer early in the second season gives it a good effort, while the simultaneous battle against Caster's massive summoned creature provides plenty of its own flash, but the final showdown between Archer and Rider and the spectacular ultimate direct confrontation between Kiritsugu and Kirei (that these two were going to fight it out eventually has been telegraphed since the first episode, so that shouldn't count as a spoiler) are the main ones which succeed. All of these and most of the lesser battles sizzle with well-staged choreography and imagery and feature animation which still must act within the constraints of TV series budgets but is still far more detailed than that seen in any of the battles in F/SN; the only one that flops big-time is a seemingly endless late-first-season battle that Saber and Lancer have with Caster's all-too-plainly-CG monsters. The content is quite graphic at times, too, in some cases to a disturbing degree, and not just in the action scenes. The anime (thankfully!) never goes to the horrific extremes that the manga version does, but it does seem uncomfortably fascinated with having male characters choke female characters to death (or nearly so); at one point this happens three times in very graphic fashion in the course of four episodes, involving three different perpetrators.

Even beyond the action scenes the technical merits remain strong, with only an occasional brief slip on visual quality. Rich, appealing character designs which give both genders something to ogle, excellent background art, and impressively flashy explosions are highlighted by vivid, nicely-toned use of color. The CG visuals are sometimes much too obviously CG, but otherwise they are used effectively, with scenes of Saber riding around on a motorcycle being particular visual highlights. Yuki Kajiura delivers a quality job on the musical front, infusing the soundtrack with suitably bold and dramatic sounds done in her inimitable style and providing (with Kalafina) the second opener “to the beginning,” a strong song paired with very fitting visuals which replaces the equally strong "oath sign" used for the first half. Second series closer “Up in the Sky, the Wind Sings” is also a strong effort, one which replaces the first season's montage of adapted historical images of the Servants with a montage chronicling the meeting and love of Kiritsugu and Irisviel. Some of the images from that are compelling enough to make one wish that their story might eventually be told in more detail in some future OVA release.

Fate/Zero has flaws, to be sure. Its first season (and to a much lesser extent its second season) all too often falls into the common Type/Moon trap of letting characters excessively philosophize, though the series assuages this a bit for Type/Moon fans by providing cameos from several other Type/Moon properties in one of Kiritsugu's flashback episodes. The first season so carefully takes its sweet time in setting things up that certain parts of it can drag, while in the second half it seems to run short on time in a couple of places, requiring events to be forced and/or cut short. Evaluated together, the result is some mildly uneven pacing over the course of the series. A handful of scenes scattered throughout are also thin enough on explanation that they may confuse people who have not read the source novel; Kariya's final meeting with Sakura in the series is a prime example of this. This series also completely reimagines one of the major flashback scenes from F/SN, though that is simply a matter of a different director's vision being applied to a scene that was never explicitly described in the original F/SN visual novel anyway. In the end, though, Fate/Zero has well more than enough great scenes and great dialogue to make up for the occasional flaws, and its strong ending does an impressive job of setting up F/SN. As both a standalone project and a prequel, the series is an unqualified success.