Out of the shows I've watched all of the way through, I'd have to recommend from the Heisei era:
Faiz (Serious & dark, with a mostly interesting plot (in the last few episodes it goes awry.)
Blade (The plot was all over the place, only really starting to get good from about 12-15 episodes in. But has a very satisfying ending and some great drama.)
Highly recommended: Hibiki, a very untypical series however, with a much higher emphasis on the character drama elements, rather than the Toku ones. The series is also missing many established Rider elements etc. But it's damn near amazing all of the way through, even so after the writer change half way through, which messes things up.
Avoid Kabuto, it's garbage.
From the Shōwa era:
Kamen Rider Black (Great start, though a lacklustre & repetitive middle run of eps until Shadow Moon appears, but then it gets pretty damn amazing!)
Others I haven't seen all of the way through but can recommend:
Amazon (Probably the most raw & violent Rider of them all.)
Stronger (A very good epic ending to a decent series.)