A metal gear type game where the AI is trained on how all players play worldwide and it adapts and evolves over time in how it stations and uses its soldiers against you and for patrols. Every time you go back to play, the layouts and movements and gear and reactions of enemy AI differ.
It will become unbeatable very fast. The problem with creating a good game AI is to make it beatable while keeping some level of realism. Trained AI will quickly develop crazy strategies which no human will be able to play against. There are many YouTubers who train AIs to play various games and this stuff gets ridiculous at exploiting game features and bugs.