While the original game is a non-free commercial title, users often look for the "Final Edition" which refers to the unofficial translation patch applied to the base game.
Monster Park 2 ~Kamigami o Yadoshita Otome~.
If you can get it for free via the demo or giveaway, there’s zero risk. The full $15 price is fair, but using the free options first is smart.
Have you tried playing the 'Mega' or 'Dino Park' versions? They are essentially the successor to the original Monster Park 2 engine.