The success of Monster Girl Quest continues to spawn imitators with a couple of games on the Coming Soon list.
This one looks like it might be interesting:
Their page can be found here.
The demo currently shows the start of the game and part of the first level, with a fairy being the only encounter available. It looks like a combination of elements of Succubus Quest, Monster Girl Quest and Violated Hero. Violated Hero is probably the closest, but without a lot of the mistakes Violated Hero made. It looks like items and equipment will play a greater part and the player can gain abilities from defeating monsters through pleasure attacks rather than normal attacks (the fairy gives a healing spell). As with Monster Girl Quest it looks like losing will result in H-Scenes as does winning through pleasure attacks. The odd thing is the dungeon appears to be a single straight line, so it might be a dungeon crawler without any exploration.
Projected to be out in October and might be worth a look.
Here's something that's out now, but is more of a Visual Novel:
Nymph Principal - The School Ruled By Succubus
It's on dlsite.com here.
It's a VN rather than a game. There are choices to be made every so often, but they essentially boil down to "Would you like to be raped by a succubus now?" or "Would you like to continue the story?" The trial version is well worth grabbing because of . . . well this:
. . . which is rather tasty. Sadly the rest of the game isn't up to the same standards with artwork - as so often with these things - being a bit of a mixed bag. Rather frustratingly, they tease you throughout most of the game with the other well-drawn succubus, but when her H-Scene arrives . . . yep, it's a trap. Grrr to the surprise futanari, although the scene is probably quite hot for people that like that kind of thing. (And I'm hardly one to talk given the various horrors I've ambushed readers with in my weirder stories).
Well worth downloading the trial anyway.
And some voice works:
Daretoku Saimin Seisakujo
Can't remember if I've mentioned them before, but this circle puts out some pretty good Monster Girl-related voice works in a similar vein to Toro Toro Resistance's releases before he put Monster Girl Quest together. Like with those releases, full scripts are included. The hypnosis part is probably baloney . . . I think . . .
And in the same vein, but been around longer:
Another circle doing voice work, although they don't appear to be active anymore. I picked up the spider girl one when I was trying to fathom out how to navigate the Japanese site. The succubus bad end one is hot. They also have full scripts included.
The artwork is by UN_DO. I wasn't too impressed with their work on the Monster Girl Quest games, but the work (mainly additional pics of some of the monsters from MGQ) on their own website is actually much better.
Plenty there to keep the filthy little black cells in my imagination sparking away . . . :)
EDIT 23rd July 2012: Something I should have made clearer on the voice works. They have scripts, but they are in Japanese. You'll need to use a translator like AGTH and be good at keeping track of where the story is (recognising words or onomatopoeia helps) to get the best out of them (and also have enough imagination to fill in the odd blank where the auto translation whiffs).