Kabuto's good, but there a really weird tone shift a bit into it that kind of bothers me, especially looking back at it. Tendou is a solid character the whole way through mostly, and Kabuto is, while a simple suit, pretty stylish, so it's no biggie.
I may be biased, but I think Fourze is a good starting series. Sure, it's a bit boring around the middle, but it's a lot more stable when it comes to plot elements and tone and keeping everything more or less coherent, plus there's a bevy of cool powers to entertain you with and the coolest (imo) 2nd Rider I've seen.
Kiva's probably in my bottom, although I wanted to like it. The biggest problem? Kiva himself. First of all, the suit actor is usually very good at matching the face actor's personality, like, when you see Kabuto, you can easily see Tendou in it, and same with Gentarou and Fourze, but for the life of me I could never see Wataru as Kiva. It didn't help that Kivat did all the talking. The body language of the two just don't match at all. The show never clarified it, but I was also confused as whether or not the Arms Monsters actually possessed Kiva when he transformed into the Arms Forms, or if Wataru would just take on the behavior of, for example, a werewolf when he became Garulu Form. The second problem was the fact that they did a horrible job at balacing the various Forms and Powers, as once Emperor Form appeared, it seemed like Kiva couldn't win a fight whatsoever without using it, rendering the Arms Forms useless. All the other series I watched allowed the Rider to utilize his older forms alongside the newer ones, but not with Kiva.
