"One who does not fight will not survive."
Kamen Rider Ryuki, unlike Kuuga, does not have one Kamen Rider; it has 13, each of which have their own goals and motivations, all of whom are pitted against one another in a battle to the death to determine who will earn the ultimate prize and have their deepest wish fulfilled. In addition, all of the Kamen Rider fights take place in the Mirror World where strange monsters that prey on humanity reside, and each Rider forms a contract with one of these monsters to increase their power, but in turn must keep the monsters regularly fed, whether with other monsters or people, or be eaten in turn. Oh, and cards are used to activate powers and summon items. Basically, Ryuki is Kamen Rider meets The Highlander meets Digimon Tamers.
Kamen Rider Ryuki is comprised of a 50 episode series, a feature length movie which is an alternate continuity to the ending of the series, and a direct to DVD special with two different endings which is an alternate take on the entire series. All of which is canon, due to time travel shenanigans.
The first thing I want to say is that I really liked Shinji Kido, the main Rider and protagonist of the series; right away he realizes that having all the Riders pitted against one another is total bullshit and he strives to get everyone to realize this and bring an end to the fighting. However, over the course of the series he finds out that it isn't that easy, that some people are fighting for very important reasons, while others are amoral or just plain psychotic, so his convictions and beliefs are constantly being tested, which creates character development, tension, and drama.
The supporting cast, whether they be riders or civilians, are generally very good. Most notable among the civilians is the reporter Momoi Reiko, who is Shinji's co-worker and over the course of the series, she manages to find out the truth of what's going on independently, and is a total badass who does not put up with your shit, not even when she's got a case of Pink Eye. Among the supporting Riders is Tezuka, a fortune teller who's fortunes are never wrong and also seeks to bring an end to the fighting, presenting Shinji with an important comrade in his struggle.
The fight scenes are very nice with a good balance of CGI and practical effects to truly create the sense of the superhuman power that both the Riders and the monsters wield. Plus, the music is really great and gets your blood pounding for the action. Furthermore, since the bulk of the fighting takes place between humans, grudges and conflicts build, creating an emotional edge to the proceedings and keeping the story strong all throughout as it builds to a surprising but in retrospect inevitable ending.
However, despite the fact that the series is overall very good, there are two points of contention that annoy me greatly; the characters of Asakura and Miho. Asakura, one of the Riders, is a crazed psychotic killer who obviously suffers from some manner of neurological imbalance. At first I didn't mind his character too much due to the conflicts his presence introduced and the way his mere existence served to challenge Shinji's ideals. However, there comes a point in the series where it looks like there may be some humanity to him, which is then quickly snuffed out. From that point on, there was no more real point to him being in the show anymore and I expected him to be killed off shortly thereafter, like several other characters had been up to that point. He was not. He survived until the end of the series, taking up valuable time that could have been used to better pace the introduction and development of other characters who showed up later on. Plus, he was also apparently super popular for reasons that continue to defy my comprehension.
And then there's the other point of contention, Miho, the only female Rider out of 13. Not only does she only appear in the movie and not in the main series, but both her characterization and fighting capability are very poor. Plus, Shinji makes a very sexist remark to her about girls being too weak to be riders, which is just completely out of character for him. Really, the movie as a whole was sub-par compared to the series, and you could skip it without losing much of anything. And I really do want to stress that the non-rider ladies are all very well characterized and realized, so I have no idea why the hell the writers screwed up Miho like that. Oh well.
So on the whole Kamen Rider Ryuki is very good, better than Kuuga in my estimation, but still has some significant, if localized, flaws.