This game has a hell of a lot in common with civilization. Huge tech trees, and expansion are the main parts of the game.
Considering Civ4 came out recently, the turn based strategy genre is doing pretty well to get such good quality games.
This game is truely fantastic, it has a very very long play time. As long as you are prepared to eventually save your game and go to bed, you might actually be able to get on with your life at the same time. It definitly has that 'just one more turn' feel.
Of course a major feature is being able to design your own space ships. This can take a minute or an hour, depending how much you like it. If you want ships which match your most recent tech advancements you'll find yourself update your fleet regulary.
Something I didn't see mentioned anywhere, but I was pleased to encounter is, when you update your fleet you can simply purchase the upgrade on each ship, and it's done next turn. You don't have to rebuild each one at a base.
The only gripe I have with this game is that it almost feels too epic. I have a life I need to get to. In the main campaign, in the very first mission you have to invade an enemy planet, but if you follow the tech tree from simple to advanced you'll take forever to get ships which can carry troops. My advice, choose the invasion tech fairly early after you develop weapons. It will take a lot of turns, but it will go by rather quickly and you'll be able to procede to a bigger more interesting map.
That's if you want to play the campaign, there's more then enough game in there to play random or custom maps without out ever going near the campaign. You'll still spend endless nights on it.