It's a credit to his acting skills. He certainly dazzeled all of Japan with his performance as Godai.
He ratherr dazzled all (woman) of Japan with his performance as bisexual enemy in Azumi, that was his actual big break.
And I think still his best performance, right next to Tokyo Tower Mom & Me and Sometimes Dad.
The best actors are for me definitively Seto Koji and Odagiri Joe, also the only ones who never made me cringe. They played their parts to the fullest and made them vivid, simply the reason I could empathize with Wataru and Godai. Especially Wataru, because it was interesting watching him blossoming.
Looking at them as Kamen Rider and their other works, I have to say that Seto Koji still stands on top for me. He is a stunning actor on screen and stage, able to act out a wide range of really different personalities (from autistic over serious to rebellious) and can effectuate all possible emotions within each of his characters, even in different ways. Also, you can give him extra tasks and he is able to perform them like he never did something else, like singing, dancing, acrobatics, sword fights, drawing, violin or guitar play. Most actors leave me cold, are not able to move me or don´t reach me with their play, but he does, always. Simply great!
As for bad actors, there are several but the worst are for me Inoue Masahiro, Nakamura Yuichi, Kato Keisuke and Hiro Mizushima. They are plainly boring. No talent to construct a character, not able to express emotions or even just different facial expressions, no comedy timing, just monotone and flat.
Most of the other actors never left an impression on me that I could say they are really memorable or I want to see them play this or that part. One exception might be Yamamoto Yusuke, who started to improve in his acting since he worked with Seto Koji. But funnily, he still tends to be a little insufficient when they are not working together. Sato Takeru never struck me as a good actor, but as one who is staged by the directors. When I compare him to Seto Koji, I never see an actual passion or interest from Sato Takeru in his parts, as confirmed in his interviews. He doesn´t conduct character studies or works on small details that would make his character more alive or interesting. And this is something good actors just do and need doing. Sato Takerus expression of emotions is missing to minimal, and even when he tries to play an outburst or crying scene, it seems contrived, love scenes are totally out of place for him. Yes, he is a good break-dancer (a whole lot better than his acting) and needed to take a few (still not enough) sword fighting lessons for Ryomaden, but only because he had to. He doesn´t needed to sing live for Beck just once, because everything is going to be mixed in the studio for him. There is actually a lot of working around of all his weak spots from the filming crew and directors, more than his fans (want to) see. Something you don´t have to do, when you have a really good actor. Sato is far away from being a big name actor, he is just an Idol that producers will hire and take advantage of as long as he has a lot of fans, the same goes for Hiro Mizushima.