Kabuto was my first, i marathon the whole show in one sitting and im glad i did that.

My first rider seies was Satria Baja Hitam, or as its better known to the world as Kamen Rider Black (dubbed in Malay).

I was 8-ish when I watched it so I didn't really get all of the story but found it cool regardless.

The Rider series I followed almost religiously was Kamen Rider Ryuki mainly for the Highlander-type plot and vicious murderous psycho Asakura Takeshi.

I just started getting into KR. I jumped into Decade, thinking I would pick up riders from there. That hasn't quite worked out as Decade led me right into W which than has pushed me right into OOO. I still intend to go back and pick up Den-O, Kiva, and some others I really liked from Decade sometime in the near future, though.

I first watched W. Shortly after I watched Ryuki.

My first series (which I just started in Dec) is W. I started down this path after Aaron sent me the Shinken Gold SH Figuarts figure, and I started looking at the rest of the line, which is mostly Rider stuff. I decided to finally check it out, after resisting for so long. Shadowbreaker recommended W, and now I'm hooked.

As far as Kamen Rider in general, my first exposures were bootleg videos I picked up at a convention many years ago of the Kamen Rider J and Zo movies. As far as my first full series it was Ryuuki. Since then I have seen every series since and have gone back to pick up Kuug, Agito, Amazon, V3, Black and Black RX. I am a total nut for Kamen Rider with Sentai a close second....

Not counting Masked Rider.
It was Faiz.

I only started watching maybe 3 or 4 years ago. Started with kuuga, but ended up watching and finishing Kabuto about midway through the series. Finished kuuga after that then watched decade followed by Agito.

As of now I'm almost done watching all the hesei shows, just need to finish blade, kiva, den-o and hibiki; all of which Im almost or around half way through.

I've seen around the first 10 eps of both the original KR and Black, but I really need to start more of the showa stuff some time

I think it either original Kamen Rider or New Kamen Rider was my first, cant remember cause I was about 5

Chronologically?
Black
Black RX
Super-1
Faiz
Kuuga
Ryuuki
Kabuto
Decade
W (best. Rider. ever)
OOO (didn't even bother to finish 'em, stopped at 18th or 19th episode)