Like all those Civ games you've played back in the day, but simplified, expanded on, and some graphics and ai upgrades.
I finally picked it up after a recommendation from a buddy of mine, and its probly one of the most enjoyable games ive played in the last decade.
Most things that were over complicated in other turn based sim games have been revised, and the tech trees have some cool things in them.
The other factions ai is actually intelligent and i never praise games ai's in this day and age EVER. I may have to rewrite this praise as i get into the harder and harder difficulties, but as it stands right now ive not seen a game play smarter then this one in its own management as opposed to the ai just getting more resources and manufacturing bonus's that it doesnt deserve.
If i have a complaint about his game its that the battles are pretty automated, and your units seem to shoot up all the enemy units before finishing one off, where the enemy ai will focus fire giving them a pretty steep advantage in combat, but so far ive not had incredible issues with this even with a mistake thats pretty big.
Id recommend this one to anyone in a heartbeat, and im a super critic on most any game.
EDIT: and ive tried the expansions now too which id also like to say are a good investment. The most recent one basically rebuilds the tech trees (in a good and unique way for every race) and gives a graphics upgrade. They even added an option to 'force ai to use max cpu setting.' This makes the uniquely awesome ai even better, and its the only company i can think of that hasnt left us with a half baked brain to play with. If you ever have trouble with this game you can always try and copy the computers tactics. How many games can you say that with?
I think diplomacy has been improved as well but not completely sure on that one. Just know the ai in this game (friend or foe) are alot smarter or more natural feeling then other games.