If the dude's favorite Rider show is Kiva, then honestly, he might not like W. Competent plotting and complete character arcs might just come off as boring after Kiva's hyperactive idea barrage.
Oh yeah, because Kiva's character development, plot concept, designs, music, and fight scenes were so bad. :sly: Hell, Kiva has by far the best opening theme for Kamen Rider ever. EVER!!
Seriously though, I find Kiva to be the best Kamen Rider series because of the things I mentioned above. For the characters, they had some of the best development I have seen since Mutsuki in Blade. Wataru started out as this shy boy who wanted to avoid everyone as much as possible and grew into a man who would do what was necessary to save the world and everyone he knew and loved. It was not just Wataru as well though, as every character in the series grew up, which gave it a different flavor from the other series. The monster concept was unique and well done. Not to mention the switch back between the 80s and 00s really gave the show a nice edge. It kept it interesting because you knew something major had to happen in the 80s that caused things to be the way they are, but there was no way of knowing what, and when it did, it came off with incredible unexpected moments. The battle scenes were well done, fast paced, kept you in the action and wanting more. If there is anything I can say that I did not like about it, it is the lack of night battles. The designs themselves were incredible, especially Maya's design and Dark Kiva has to be the best KR design ever. Megumi, while at times an idiot, was able to hold her own, as could her mother Yuri. I even grew to like Nago, and I kept hoping he would die until the last few episodes of the series when he really showed that he was not a dick. The musical aspect of the series with the violin was a highlight for me, as I have not seen a violin used in a show for a long time, if at all. It brought a nice touch, and I loved one of the musical pieces played on the violen that I wish was on the soundtrack. Otoya was an interesting and tragic character. Lastly, the series had an ending that was complete. It did not leave off on this crapshoot with 3 of the main villians still alive. It completed its story, and built up a future that was going to be good, but would never be truly peaceful (true peace is impossible).