Kuuga is a great show. It is not very toy-heavy which many Kamen Rider seasons later are. It has a very slow pace which some might not like. Warning: Do not watch this show thinking that it is going to be campy like recent Power Ranger seasons. There are a lot of episodes depicting violence and murder.
However, due to its slow pace, it can balance the story and characters well. The characters are a good part of the reason why this show is good. I am going to talk about the major characters in the show.
Our titular hero, Yusuke Godai, is optimistic about everything. He fights as Kamen Rider Kuuga to protect people's smiles with his trademarked Rider Kick, and afterward, leaves the battle with a thumbs up. I believe the writers made him so positive is to balance out with the dark tone of the show. He is a very realistic main character, acting similarly as you would if placed in the same situation. His relationships with other characters and his journey throughout the show are very good, including Kaoru Ichijo.
Ichijo never gained the powers of a Kamen Rider but still alongside Godai. He is a police inspector who is tasked to lead a militia of other police officers against the bad guys, the Gurongi. In the beginning, the police were powerless to stop the Gurongi, leaving only Godai in the fight. However, the police officers' arsenal later grew and they became better equipped to handle the Gurongi. Even without powers, Ichijo was able to take down one of the stronger Gurongi, thus making him one of the more important characters in the show.
As my closing remarks, Kamen Rider Kuuga is an excellent show. The characters were all useful to the show. I recommend that you watch this show.