I'm making one as a hobby project alongside my day job.

It's a debate chat game where two humans debate on a topic and a biased AI judge picks a winner. Over time players compete for ELO rankings like in chess or similar head-to-head competitive games.

I'll probably make a blog post someday about what's been involved but I think the points in OP are spot on. I've been struggling to make the format feel fun and lively. Two things really helped compared to my early versions - real-time streaming of the other person's arguments so you're not just staring at a timer while they're writing and very very short rounds so you get feedback and results quickly.

The costs are a bit high but not terrible for a hobby project that no one really plays. My unit cost is around $0.008 per game if an NPC is involved and around $0.004 if it's between two humans. I could probably cover that with really intrusive ads but I'm hoping to get enough users paying for cosmetics (speech bubbles, profile pictures, etc.) to help subsidize the rest of the platform.

I've also tried a version with AI NPC opponents and it's much less fun than playing against real humans for reasons I can't entirely articulate. The AIs just don't make for very interesting debaters and the wins against them feel a bit shallow somehow. Right now, I've got NPCs on the game which you can opt into debating if you spend more than 30 seconds in the matchmaking queue but I hope once I get proper player counts I can disable them entirely.

I'm super biased, but proud of how the game has been coming along. Will make a show hn post someday but if anyone's curious my alpha version is live here: https://letsarg.com