Endless Space 2 is cool, probably the only 4x game that does diplomacy in a way that works and where all of the victory conditions feel like they're equally competitive. The alien races are suitably diverse too, with only 2 human factions and everyone else ranging from samurai ostriches to sentient rocks. The sci fi aspects are also good - terraform or destroy planets, build massive capital ships that can convert into orbital stations, advance to a post-singularity consciousness and leave your bodies behind, etc. I've lost tons of hours to this game both in vanilla and with mods, 9/10.