Not yet playable. Great potential. Best choice for play by e-mail.
If you happen to have played Space Empires 4 in multi-player with friends you'll be certain about how addictive this game mode can be.
Playing over the e-mail is fitting for people lacking fast connections and time to play on-line and it conveys a very funny experience without forcing you to make rushed decisions to overpower the speed-clicking skills of you competitors.
The AI is crap, this game is made to play via e-mail against human players. The single player game mode is just an extension to the tutorial, and it should be considered just an add-on, not the main feature of the game.
The game is too bug-ridden to be playable, even in multi-player.
You'll have to wait for a patch or two...