Well it seems that I have stumbled in Den-o fan territory.
That's not the same thing, at all. Being able to realistically portray a vastly different set of personalities takes a lot of skill and talent, you won't find that every actor has that.
Look at the series you're watching, this was Den-O where exaggeration was the norm, so it's perfectly acceptable, of course that's not to say that anything goes, but I thought Takeru did a great job. How was his mimicing poor? So what if he didn't use his own voice? He studied those voices and he pulled off all the mannerisms and facial expressions in a great manner, he was his Imagin just as much as he was Ryoutarou.
It's not a difficult task, all he did was the Imagin's respective poses and let the Seiyuu take care of the rest. It wasn't done well compared to the superb Suit Acting done by the suit actors. Whenever Ryotaro gets possessed I don't feel that the characters were a part of him but just Takeru doing bad impersonations of the Imagins.
He's supposed to be an actor, the suit actors are stuntmen, and if stuntmen can pull off a more realistic character than him, really that shows you how bad most of these new-gen actors are. Ryotaro is the only part that Takeru had 100% control of. He had no one to base that off of, no help from Seiyuus and all he could do was transpose his voice by 3 octaves. His range as Ryotaro is as one dimensional as Kento Handa. Atleast Takumi felt like a real person, Ryotaro was a joke.
I see your point of Den-o being exaggeration. A lot of Rider characters are "exaggerated" such as Tendou with his arrogance and Shoichi who is constantly happy. But even if the Imagins, who worked more like cartoon characters, managed to weave through different emotions well, in a realistic manner. Ryotaro, like I said, was one dimensional.
How did it damage the show? Like I said, Den-O itself was vastly different from any Kamen Rider series before in that it was a comedic exaggeration and that's what they did with Ryoutarou's character. Sure, it may not have been the best at the start, but Takeru Sato certainly made that character his own as time went on and he found his footing.
This show may not be filled with extraordinary actors, but I still found him to be the weakest link. Nakamura follows close behind. He's the star of the show and he really didn't manage to capture me as an audience. Wataru for the most part is a similar character, but I can care for Wataru. This might be the problem of the script, but like wise man once said, there's no small parts just small actors. He didn't make the character his own. I am sure they tried, in the beginning, to promote Takeru and have the Imagins play the supporting role. But those guys broke out, they were a hit, and they now embody what is Den-o and Takeru is just piggybacking on their success.
How did Ryoutarou not act like a hero? Almost every extreme he went to was for the sake of others. When his Imagin were starting to disappear, he blamed himself and tried to train himself, when people were forgetting Yuuto, he tried putting more of the burden on himself so Yuuto wouldn't have to fight as much, in the first episode he says "I may not understand everything that's going on, but I understand it's the right thing to do", heck, he let the guy that totally kicked his ass all over the place see his mother one last time before she died. Ryoutarou may have been weak, but he was certainly as big a hero as Kamen Rider has ever seen. I won't even address the Shinji comment since I've always thought Shinji himself was a failed character.
I find the term
Hero is thrown around too lightly nowadays. Just because a character is self sacrificing does not make him a hero. There's a sense of chivalry and nobility, in my opinion atleast, that comes along with the idea of being a hero I just don't associate heroism with just selflessness, because there's much much more.
Ryotaro felt senseless, and well clueless for the most part. A goody two shoes who was just willing to do things for people. That to me doesn't make him a hero.
Shinji was similar to Ryotaro in the beginning. Shinji was naive and wanted to save people for the sake of peace. But he started to grow, something Ryotaro never did, he started to question himself and started to struggle in his quest to be a hero.
I mean these are tv shows, they are for entertainment value. I want to see heroes fall and have conflicts with themselves. Shinji worked will because he learned the horrors of being a hero but in the end he accomplished want he set out to do. He became a Rider when he saw a little girl lose her mother and he died saving a mother and daughter.
What did Ryotaro do? Whine alot to Yuuto. Cry when the Momo and the others began disappearing for the 6th time again. It was just poor scripting and acting for the most part. I did not like the Ryotaro character at all. I just don't label characters who do perform these so called "heroic deeds" to be heroes. They need a reason behind it, a driving force and a will to save people for the greater good of things.
You know, its the same reason why I don't like villains that only want world domination. The best villains are the one you can understand, either sympathize and perhaps empathize with. This goes for being a hero as well.