Sadly RAGS hasn't had a huge amount of popularity outside of those two aforementioned sites. RAGS has a lot of promise for general adult games, given that it's graphics-oriented and reasonably easy to learn (although you do have to pay for it). Perhaps any budding games creators reading this might want to give it a go?
You'll have to register to browse the Hypnopics forums, although some of the games originating there are mirrored in other places (such as aifgames.com or the AIFArchive). You can browse TFGames without registering, but you will have to register to download anything.
As mentioned, most of the games on those two sites tend to be either buggy or incomplete (or both), but I'd recommend Rough Landing 1 (just about the only complete game on Hypnopics I can think of, and quite good too; the sequel is currently in open alpha) and Bodywerks (incomplete, but excellent production values if you don't mind the author's taste in fetishes).
While there aren't any AIF games that rival SD3 in terms of graphics or size (it did take two years to create after all), there are a few that I'd say are as good or better in other areas. Sex Artist and Tomorrow Never Comes are two that spring immediately to mind, but there are others. Take a look at the Inside Erin newsletter (
http://newsletter.aifcommunity.org/) if you're looking for suggestions for what to try, as it has an index of reviews.