Well, it's even darker than the way the TV show began, for one thing, and even if Ichimonji's introduction does, as in the show, bring some moments of levity, the darker parts are still just as dark. The art, being pretty old, is dated in quite a few panels, with proportions and such, but when Ishinomori wants to draw something detailed for an emphasis or large panel, he does it well. Kind of like a proto-Kurumada (Kurumada is the mangaka of, among other things, Saint Seiya and Ring ni Kakero) in that respect, I guess.
The story (which is entirely separate from the TV series; kind of an AU) is very streamlined and fast-paced, and doesn't slow down or stop much at all; which fits the impression they're trying to give of Kamen Rider--he's a very fast-moving, energetic kind of hero. It gives me the same kind of vibe, in that regard, as the early 30s/40s Superman comics. Characterisation is still achieved well within this streamlined frame, though, and while nobody in this manga is going to top your all-time favourite characters list, they're all well-defined and likeable enough. The fast pacing also doesn't cause any problems with plot holes like might potentially occur, with the possible exception that while it's implied, it's very vague about the fact that absorbing wind is what activates the Rider's powers (hence why he transforms by driving/running/falling especially fast) until finally stating it explicitly in volume 3. As in volume 3 of 4. Three-quarters of the way through the story. Ah well, I already knew that was how it worked (at least, in the TV show it worked that way until he got upgraded and used the Henshin pose thing instead), so I don't know if the implications are clear enough or not for someone who isn't already familiar with Kamen Rider.
And building on something I just mentioned--it's only four volumes long, with each volume only containing one to three chapters. With that said, though, another parallel with Kurumada is that these are some long-ass chapters--volume 4 is comprised of a single chapter of over 100 pages. Still, volume-length is about volume-length, consistently, so yeah, it doesn't take long to read at all--it took me just under two hours to blitz through the entire thing.
All in all, I don't know if I'd give it a screaming recommendation, it wasn't one of the all-time greats, but it was overall pretty good. I enjoyed it quite a lot. So...uh...yeah. That's my review.
