Okay, so I don't keep up with Key's newer releases, so shoot me.
I edited the first post to include a story synopsis, the approximate price (man, H-games are getting expensive), and a pretty hefty requirement. I don't remember any game needing 20 gigs, except for Phantasy Star Universe, World of Warcraft, and maybe GTA 4.
Edit: I notice the reply/modify textbox auto scrolls upward. Very irritating.