*interest in thread intensifies*
Off the top of my head, I know of HHS 3 and Slave Maker 3. Free Cities has some herms/futas in it, though they're nowhere near the main focus, and if you want big dicked ones, it'll either take a good amount of rng or renown and money. Shemales/Dickgirls are much more common, if you're up for that. If you want, you could also give the games on fek's furaffinity a try. He's done his own flash game, Rack, as well some work for JasonFex, in which you can choose some of the characters that are herms/dickgirls to play with.
Is language too much of a problem? I like these two from Tsukinomizu, but they're Japanese.
Lilim Union http://www.dlsite.com/ecchi-eng/work/=/product_id/RE103157.html
Lily Knight Saga http://www.dlsite.com/ecchi-eng/work/=/product_id/RE123426.html
You can find a "walkthrough" at hongfire. And, well, despite having a lot of scenes involving futanari, they focus more on tentacles and yuri scenes. So I don't know if it would interest you.
Besides that, Misakura Nankotsu/Harthnir launched a lot of visual novels with futanari heroines.
Nearly all these games are gonna be Japanese.
Futa is largely a western fascination, it's just there's actually a market for Japanese things of all sorts and not so much for the west. You're stuck with a paltry few translated games (Village of Nightmare comes to mind) and a bundle of on-a-blog-somewhere English-developed games which are few in number in the first place, let alone quality.