Okay, so I'm a decade late to the party, reviewing a game so old I have to turn down my monitor resolution manually for it to run properly. But I'll be damned if it isn't fun!
The differences between the playable factions in the game are more than just the typical cosmetic or minor-boon types you find in many 4X games; every single faction has a wildly different playstyle because they all employ different forms of interstellar travel, and have different spreads of tech trees. There are a lot of random factors to the game that make every game different; planet hazard ratings, available techs, encounters, and star locations.
But it is where there is NO randomness that makes the game stand out: Combat is done entirely in real-time with actual ballistics and NO die rolls - the only randomness comes from weapon spread cones. Population growth is predictable, travel speeds behave the same every time, and weapon damage is fixed. This perfect balance of where to have randomness and where not to is what makes SotS so enjoyable; despite the random factors, skill and tactics will always have the final say in victory.
Toss in the amazingly detailed lore by Arinn Dembo, and you get a 4X game with a surprisingly engaging setting. The alien designs avert the usual boring "bipedal humanoid recolors" that plagues sci-fi; you've got clever reptilians, long bird-dragon-things, sentient insectoids, telekinetic cetaceans and rabid marsupials.
Pity about the sequel, though. At least the spinoffs (The Pit, Ground Pounders, and Freehold) make up for it!