I don't know what it is about Interstellar Space: Genesis but I'm addicted to it. Everything seems to click for me. I feel like I'm playing what MOO3 should have been.
The game has garnered quite a few comments along those lines. While so many have tried their hand at creating a "spiritual successors" to MOO2 and failed (or at best, had mixed/uneven results), it seems IS:G may have finally succeeded.
You can tell the devs truly gave a lot of thought to what previous 4x games did -- and did not -- get right, and then designed/built IS:G accordingly. It doesn't alter/reinvent the genre the way
Stellaris (for better or worse) has, but refined the existing formula with some neat ideas and well-thought-out mechanics (such as the exploration system, and how Leaders work).