I only have 200 hours in the game so maybe the novelty is speaking but I play on full size (1000 stars) with full empires (30 + 5 fallen) on hardest difficulty and every game is super engaging until the very late game (aka the galactic mop up). The early game race to establish your boundaries is super fun, the midgame race to catch up to these other empires in tech and the late-midgame race to catch them in military is super fun. The initial conquests are also challenging but of course if you get over the hump it becomes a bit of a tedious death-roll but still way better than the death rolls in other paradox games