Oh, for the Showa Kamen Rider series.
I might recommend starting with the duology of
Kamen Rider Black & Kamen Rider Black RX (already shared the videos on the previous page) and skip the original 7 series that preceded them. I wouldn't say the previous 7 series were bad though...but how do I say this?
The comparison would be the same like if you were watching Godzilla showa series vs Heisei & Reiwa series. (sometimes, it was rough to watch at some aspect of it, haha...so I definitely wouldn't recommend it for the first timer

).
So, Starting with
Black & Black RX is equivalent with watching Godzilla for the first time with "
Gojira 84" or "
vs Biollante" onwards.
And I apologize beforehand but I also really wanted to show the day & night differences between
Black RX and Masked Rider (the American adaptation of
Black RX)...because heard that a lot of fans in the west had making fun of it for quite sometime (but after seeing how they butchered
Black RX and changed it into a sitcom comedy, I wouldn't blame them).
True story... the author of Kamen Rider, the late Ishinomori Shotaro-
sensei had expressed his big disappointment in the Saban's adaptation. (To this day, I always thought that Saban's Masked Rider was what tarnished the brand and the name of Kamen Rider in the west. Often I read that KR is just a cheap knock off of Power Rangers...and tbh, it was quite bothered me to hear that).
So yeah, I hope upon watching the original series and also the upcoming brand new series (Zeztz) that will be streaming simultaneously with US market, the new fans will grow and redeem their views on Kamen Rider.