Ancient Space was awful. It felt a bit like Warcraft 3 in space, but somehow way, way worse.
It was clunky in both ui and design. What could have been a spectacularly intricate and thoughtful game became a rather haphazarded mess. Stellaris is so much better, but it's an entirely different gaming ethos with completely different goals and priorities. Besides, Ancient Space used unity which is rather awful (but is improving in leaps and bounds). Stellaris lives on the inhouse engine which speaks C++.