I bought GalCiv2 (and its expansions) because I heard a lot of good things about it... how fun it is, and how smart the AI is.
But within a week I found the AI dumb as a brick, even on the very high levels. They get stronger only because of their starting bonus on higher difficulty levels, and that they know where the planets are so they get to colonize worlds faster. Their abilities to judge their strength against the player is laughable (declaring wars when they really shouldn't, surrendering to another AI when they can still put up a good fight). In fact, the most serious harm they can do to me is when they surrender very early to another AI, creating a super large AI faction in a single turn. The AI also don't know how to wage war properly, I often see them sending nothing but fighters to my outlying planets, which all got shot down by my star bases before they can attack.
The planet management is quite boring, because there are not a lot of things to decide. There's really only five types of buildings - money maker, factories, research, growth, morale. They don't have drawbacks, you just need to keep tabs on the amount of money they are costing you. Once you decide what a planet is for (money, weapons or research) the planet management may as well be taken over by an algorithm.
The only plus for GalCiv2 is the ship designer... but that's just a gimmick.
My 4X game of choice is Fall from Heaven 2, running under Civilization 4's engine. I haven't played in a while... I was waiting for the AI upgrades they are working on, to teach the AIs how to use spells properly.