I tried Ishu Aigan some time ago.. well, I shouldn't have. Anyways here's my review.
So, do you like frogs, slugs and reptiles? Have you ever thought about them fucking you? If so, then you're in luck as this game will show just that. The art in this game is decent enough, but you'll have to read a ton of text to get to it.
Iirc the story is as you would expect from H games - not great. But at least it is alright in this game.
Now, this game is IIRC a VN in every sense of the word. No real choices, you the player is basically there to simply view the scenes and click next when you read the text. It would have been better suited for an Anime.
Take my review with a grain of salt as it is some time ago that I played it. Honestly, I didn't find it interesting at all, and deleted it shortly after.