I love and truly adore a niche Space RTS game called "Star Ruler" that came out ~~10-odd~~ 14 years ago. With the 'Galactic Armoury' mod, it's so fucking cool. You get to run your empire while designing and build ships of increasing complexity, and eventually insane sizes, custom fleets with a mothership with a repair bay with a big laser (or ten thousand tiny lasers) or you can harvest/blow up a star and eventually you can build giant thrusters on your planets and fly your planets around like they're spaceships and fill them with rocket silos and shield generators and ugh. The only game I've enjoyed to seriously incentivise fundamental tech tree specialisation, too.

Star Ruler 2 had none of that, and made me spend most of my time dealing with a frustrating diplomatic cards system, and it had a decent ship builder, but it just wasn't the same. It's probably objectively an okay game, but my disappointment was huge, all I wanted was a better engine, sleeker UI, tighter interfaces, nicer graphics, etc. and it was instead basically just a different game.

I still regularly replay SR1, something about it captures an aspect of my imagination nothing else has.