Similar to Kuuga, but this time Eiji has a backstory reason for him wanting to help everyone else.
The other characters like Ankh he is a Greeed who for some reason is only an arm, he takes over the young police officer's body so he can move freely. Ankh is trying to get more core medals so that he doesnt become weak and another desire. He helps OOO by giving him medals to fight and knows knowledge of their powers so he can make good combinations with random medals. The sister of the officer was the girl with abnormal strength and she wants Ankh to return her brother Shingo to her, but she doesnt know that if ankh leaves Shingo could die. So she takes both of them to where she works to live so she can make sure her brother is ok. Then there is her boss Chiyoko who is very hyper and active, she is the type of boss that likes to get friendly with everyone. In the foundation which is named after the boss Kougami they look over all the cell medals and collect them for unknown purposes. Kougami is a secert man, but he loves desire and new beginnings that is why we hear him say "Happy Birthday" a lot. There is Satonaka who is mostly Kougami's secetary she doesnt do much, but she can help in big moments. Gotou is a solider for Kougami and he wants to protect this world anyway he can, but through out the story he finds out that he cant do things alone. Maki is a scientist for the foundation he makes inventions that help OOO mostly, but he doesnt care for beginnings, but for the ends. Then there is our secondary rider, Kamen Rider Birth who is Akira Date a man who works to fight so he can reach his dream of 1 million yen (I could be off). For the Greeeds there is Uva who is mostly doing what he did back then he is only doing what he wants. Kazari is different he knows the world has changed and he wants to experiment with this. Mezool is like Uva, but she is more complex cant say how because it will spoil the series. Gamel is the last one of the group and he acts like a child all the time and always hangs around Mezool.
They do share some similarities, but there is more original ideas with this series and its not a bad thing.
Cons- There is a little too much filler and not all of them are great, those episodes get in the way of the villians at times. Also what gets in the way are new additions of villian and the series can lose focus on some of them at times, but at least the good guys arent forgotten. There were also some useless moments in the series like the CLAWS Scorpion which was used once and thats it. The build up for the final episode felt a little rushed and not as dramatic at times for some characters because they were sometimes forgotten (expect for some though).
Good villians, but could have been used a little more
Netural- OOO has the most forms in the whole franchise because of his form relies on three medals and there are like 7 sets and each have a head, body, and leg. Different type of combinations help keep fights feel fresh, but sometimes they dont really do that a lot and heavily use the main combo forms a lot at times. Birth was a great rider, but the series made him look weak at times, but that is for writing purposes because Birth was made to fight Yummies, not Greeed. There can still be great fighting moments for Birth though.