Since finding monster girl games that are actually released and worth playing has proven impossible, let me suggest a few that are still in development!

1. Hero Quest Video Game
2. Monster Hero Game

Hero is a three-dimensional game based on Monster Girl Quest. It is currently in production. One is Hero, an E-rated adaptation which will be altered to fit an M rating, and the other being Monster Girl Quest 3D, the unchanged adult rated version. The adult version will be a nearly exact 3D clone of the story, characters, etc. From Monster Girl Quest, though Ntelliware has hinted at a few minor additions. An AU of Monster Girl (Monmusu) Quest! Where a second companion with a dark past works with Luka on his quest to the Monster Lord's Castle. With yet more dissenting viewpoints, how will Luka overcome all of the views which keep his dream of coexistence out of his reach? (Non-hentai version. Minimal non-canon/OC relationships.

Quest Failed – https://www.patreon.com/user?u=3084036

A visual novel in English with monster girls! And voice acting (that’s actually good)! There’s a demo available on the Patreon page and the full version will probably be out soon. The demo is fairly light-hearted, but that doesn’t mean the story won’t go in other directions. I’ve been backing this one on Patreon since it was announced since I’d love to see more monster girl stuff being made outside of Japan.

Hero Quest Video Game

Monster Girl Island – https://www.patreon.com/monstergirlisland

Another English monster girl entry, but this one is a 3D game. The models and animations on the sex scenes are pretty good, which is what counts. The rest of the game is still in early development and very raw. I’m not sure it’ll ever be a good “game” but I’m happy to support it on Patreon just to see more 3D monster girl sex. There are demos available to download and check out. It even has VR support if you’ve got a headset, which is probably incredible.

Zell’s game FOBS – http://zell999.blog.fc2.com/

Unlike the other two recommendations, this one is Japanese and practically text free. It’s a side-scrolling action game with great pixel sex animations and is regularly updated with new monster girls. The game itself keeps improving, but it’s still fairly bare-bones in terms of actual gameplay and things to do. There should be an update relatively soon if you want to hold off playing it. Links to the game and passwords are located here: http://forest.x.fc2.com/download.html

I’m hoping these three games in development eventually turn out great because despite the good number of monster girl game releases, most of them are really bad. The ones with redeeming qualities are hard to recommend to anyone that doesn’t speak Japanese. Here’s a short list of releases this year that weren’t 100% terrible at least:

もんむす!逆レイプ学園 Another Dieselmine release, but this time a VN. Good art as always, but stale and boring.
犯されヒーロー～みんながボクの精液を狙ってる…!?～ If you aren’t tired of Violated Hero games.
魔立ロリサキュバス妖魔園 Monster Girl Kindergarten. Obviously loli. Made by the guy that did the MGQ Delicious! vore titles, although this game is light on vore. Playable with a walkthrough I guess.
モンスター娘百覧Vol.1 If you don’t follow Torotoro, maybe you missed Hyakuran coming out. Short stories in VN format. It mostly sucks.
堕落乙女異聞―堕ちたる勇者と真実の魔剣― Fallen Maidens Monster Girl Encyclopedia game. RPGMaker walking simulator with pixel sex. Incredibly disappointing. The pixel art is heavily censored. Pixellated pixels. Thanks Japan.
迷宮踏破 MonsterGirls If you remember Desire Dungeon, this game is Desire Dungeon meets Etrian Odyssey. The gameplay is all right, but if you want gameplay, just go play an Etrian Odyssey game or any of the dozens of great dungeon crawlers. H-content is mediocre.

Muff Diver

Gaming Legend & LoneWolf

Monster Hero Game