I'm right in the middle of my 4th game. Extra large planet, so it takes a long time. My strategies seem to work very well in the easier levels, I haven't tried the tougher ones yet, but I think I'll step it up on the next game. In the easier game modes I completely dominate all other civilizations.
If you do decide to use nukes, save your game just before you launch an attack because all hell will break loose. That way you can always go back to the save if you don't like the way the game is turning. If you use nukes be prepared for war with every other civilization still in the game...
Damn addicting game.