Depends on the game to be honest. A visual novel like
Oral Lessons with Chii-chan is a game with still images that you choose options, but I'd say most of the games on Fakku are 3rd-party games from other publishers made in RPG Maker and use an RPG battle system in one way or another but then have still images for different cut scenes. If you want some recommendations:
Yamamoto Dragon Ball games: these games are all made by someone who can copy the Akira Toriyama art style perfectly. The games themselves are not that fun as they're just fetch quests and rock paper scissors, but the hentai is amazingly and smoothly animated. Also features galleries after you beat the games.
False Myth: if you want an actual video game, this is it. A very cool RPG with a card-based battle system. Features pixel-graphic animated hentai scenes.
Summer Memories: a time management game where you choose different activities to do during the day as you work to seduce your aunt and cousins you're staying with for the summer. There's also DLC for this game. It's a fun game and there's a lot to it. The scenes are animated as well iirc.
Ideology in Friction: RPG Maker game but a pretty well-made one. Also has DLC.
Abaddon: Princess of the Decay: horror RPG with NES style graphics. Difficult but features tons of CGs that you can view in a normal art style or pixel-art style.
Honey Select Unlimited: robust character creator software that also lets you bang the characters. Has DLC that adds a bunch of stuff.
And those are some recommendations. If you have any questions feel free to ask but it's been a while since I've played these games.