Just to add to my previous post, victory conditions often lead to strange AI behavior. Nothing bothers me more than having the entire galaxy start to hate me in a game like Endless Space just because I have the highest score. Suddenly other empires are throwing their ships and their lives away because my empire is the biggest and the most advanced. Suddenly trade isn't an option anymore, because nobody is willing to trade with me. The scope of the game narrows and narrows until I am basically punished for not finishing my conquest of the galaxy, even though I am playing as a 'pacifist' empire who has only expanded because other empires wanted my systems and they underestimated me.
Because if there is a score, or victory conditions, it is basically a given that the AI will be playing by the same rules, and have the same goals. Which may provide the AI some direction initially, and may prevent the player from achieving their victory conditions too easily, but it also removes (by necessity) the potential for empires that are more concerned with survival, with prosperity, with culture, with diplomacy, with just concerning themselves with their own empire's longterm stability.
I want to see small, economically powerful empires that have no interest in fighting and cheerfully dump money on their powerful neighbors to fight on their behalf in lopsided alliances against an attacker. I want to see large empires that don't automatically want to gobble up their neighbors merely because they want to work toward some domination victory. I want to see quiet, scientifically advanced empires who don't immediately turn that technology onto their neighbors, but actually share it with others and build up a respectable reputation as peaceful and helpful.
You never see any of that in any 4X game, it's always the same thing. Technology exists to help you crush your enemies. Trade exists to help you crush your enemies. Diplomacy exists to help you crush your enemies. And that is all the AI knows how to do, even the empires whose race-write-ups describe them as peace-loving pacifists are only marginally less likely to turn on you, and that will go away the moment the AI determines you are on a path to win. Because even pacifists want to 'win' the game.
Victory conditions are bad. I don't even like victory scores, let me tell my own story. But if you have to have one, bury it, like CK2 buries it.