Honestly, with Proton, the answer is "many of them", so it all depends on your personal taste!

My current highest Steam counter goes to Stellaris, the Paradox 4X space strategy title.

Technological Journey!

It's a nice GTCE + Gregicality pack that's more involved than Nomi but isn't quite at GTNH complexity. I'm chipping away at it whenever I'm in the mood.