Cool series. A definite opposite to Kabuto.
I'm a big fan of Kabuto.
This kamen rider series is like an exact opposite of Kabuto.
Where as Kabuto was mostly serious with some funny moments added in and has a skillful and badass main hero (tendou souji).
Den O is the opposite. Most of Den O is goofy and comical. It doesn't take itself very seriously and most of it just funny comedic things.
The main character of Ryotaro is annoying and wimpy. He's the definite opposite of Tendou who's skillful, cool, calm and in control.
I still personally prefer Kabuto because of the better story and main character.
But Den O is also pretty fun.