Now, let us count up your sins.
Shotaro Hidari is a self-proclaimed "hard-boiled" detective who more often then not comes off "half-boiled". Phillip is a strange young man with all the world's knowledge in his head, save anything to do with his own past. Akiko Narumi is their self-proclaimed chief and daughter of Soukichi Narumi, Shotaro's mentor and Phillip's rescuer. Together, they form the Narumi Detective Agency, dedicated to investigating cases involving the strange, drug-like devices known as Gaia Memories, and when someone uses a Gaia Memory to become a super-human monster known as a Dopant, Shotaro and Phillip combine to become the defender of Fuuto City's tears, Kamen Rider Double!
Kamen Rider Double is much more theatrical, comedic, and quirky than the previous Kamen Riders I've watched, and this is due in no small part to the main character Shotaro, who is constantly trying to live out the narrative of the Hard Boiled Film Noire Detective like his mentor Soukichi and constantly falls short of that mark, letting his emotions and sympathies get the better of him. This creates a theme in the show of images and masks, of heroes, villains, and everyone in between trying to project a certain identity or role in their lives in order to deal with it all, and it plays out very well in my estimation.
The main gimmick of the series is that when Shotaro and Phillip combine into Kamen Rider Double, the suit is split down the middle, each side a different color corresponding to which Gaia Memory that person is using. Gaia Memories look like flash drives, just fyi. In any event, by switching in different Gaia Memories, Double can use up to nine different forms, and that's just to start with, though they don't create nearly as many forms as they could have, which is good. The gimmick works well as it emphasizes quick thinking and teamwork between the two heroes, having to coordinate their actions to a single plan.
While Akiko is definitely much more quirky comic relief than previous leading ladies in Kamen Rider, the fact is that she does periodically manage to contribute to the groups efforts and be awesome, despite being only an ordinary girl in a world of monster men on motorcycles. And while they don't stick around, there are plenty of female guest characters of the story arc who are well done, and some of whom I would have liked to have been able to stick around for longer in the show. Oh well.
The big bad villains of the piece are appropriately enough, a mob family. The Sonozakis who manufacture and distribute the Gaia Memories to the general populace of Fuuto, and while they seemingly get along well enough at first, over time you learn just how truly screwed up all these people are, and it is very interesting to watch.
Overall, the show is very good, but the first few episodes are a bit weak, and it took me a little while to be able to see Akiko's awesomeness. Definitely a Rider I'd recommend to anyone.