Welcome aboard.
As for Ryuki yes it is a great show but I recommend at least watching Kamen Rider Black and Kamen Rider Kuuga first to have a foundation for the series. After that watch Ryuki, Gaim, and all the other seasons. I won't tell you to watch all the Showa shows since that would be too much so at least give Black and Kuuga a go before watching Ryuki. Or if you want something that is true to the roots of the franchise while being new, watch Kamen Rider W(pronounced Double).

Watch Gaom second. If u watch it first it'll ruin everything else for you

It moves at breakneck pace while having fun with a hilarious gimmick
All other shows move like molasses

Here's a tip: Watch what you think looks interesting first.
Gaim isn't the epitome of KR storytelling and Kiva isn't as bad as the plague. If you think Ryuki will be good, watch Ryuki.

All series has it's ups and downs. Please don't listen to Gaim fanatics who believe it's impossible to surpass, as it has some of the worst characters in the second half of the series all tangled up in a mess of a plot that relies on poorly done twists rather than a natural story flow.

I would reccommend watching whatever you think looks good.

If that happens to be Ryuki then I would super reccommend it and hope you enjoy it.

I EXTREMELY recommend Gaim. The best one bar non.

Double is also great, and so is Dragon Knight (it's american so some people here don't like it but. It's pretty great).

I also like 000s and Decade, but a lot of people hate Decade too because of "lore inaccuracies" or changes.

Actually, there is little in "Lore inaccuracies" since the show takes place primarily in alternate universes (Though there is one major inaccuracy that completely derails one of the most sincere Rider's story line).
I hate Decade because it's a bad show covered in flashy action.

If you want to start watching Kamen Rider, I recommend starting with W. To me, the Neo-Heisei shows are a great jumping point for beginners. It helped me ease into the rider series a whole lot.

I think Decade is a very interesting and worthwhile show that ultimately did more good than bad by literally and figuratively bringing back the previous Riders back to public consciousness, even having its themes based around it.

But otherwise? Yes, Decade is not a newbie friendly show either. Also have to agree that Gaim isn't all that great and lets just leave it at that.

To actually recommend a series rather than just be an asshole, I would recommend:
Decade for it's ease to jump into (No one knows what the hell is going on, regardless of whether you've seen the other series or not :p) and tons of flashy action
W/Double for it's coherent story and fun characters. It's a great series that balances it's story focus well.
Gaim for it's interesting story and darker tones. It has quite the tonal shift in the end, but it's a great series as well.
Ryuki, for having a complex plot that is told well, along with characters that are easy to love and an interesting concept.

I want to recommend Blade, but it's weak start, terrible video quality, and sub-par subs makes it hard for newcomers to get into as a first series.

I don't feel the past riders needed to be brought back into public eye, as they were still known enough. It's not like we needed to see characters like Blade or Den-O, only 6 and 2 years old, return so soon. And there was little love for Showa, as only Amazon and Black/RX got love in series.

However, I'm on the opposite opinion. I think Decade is a great gate way series, to be honest. It presents the Riders' original stories with tweaks and changes. It can spark interest for newcomers. It's mercifully short, too.