1. Going to war and convincing others to fight a war.
Ai doesn't take ship range into account when declaring war, it seems to just judge military power above being able to invade.
2. Thats really a hard one going to really anything beyond 300 turns isn't fun if the AI isn't smart enough.
3. Galciv 2 was good, at least in terms of spying, influence was a bit better for UP. Ai didn't have to worry about correctly placing tiles. Sins of a solar empire was great in terms of the content from the xpacks and the pricing. Civ 4 was good with all its content and Civic options for government ideology in Galciv3 really just felt like the whole good vs evil which I really don't like. Civ 5 was much worse then Civ 4 but its combat was fantastic and made it rather fun and worthwhile.
Galciv3 Really suffers from poor combat with a simple attack and defence system, though the addons you can later get seem to add depth they cost valuable rare resources. Would love to see the combat further improved and the movement and range tweaked. Fleet engagements feel a bit odd with the logistic system that makes it a bit awkward, a tile should be limited to the logistic cap and more then one fleet should be able to attack a target if they're adjacent to it.
Movement is far too free, theres no choke points, military starbases should stop movement of hostile fleets unless they attack it. Ship range should go off from the star systems so that deep space with almost no stars are hard to explore. Even a supply system so fleets can go outside the range for a few turns before needing to recharge might make that fun. That might make maps like tight clusters and spiral much more interesting and tactical. Might make the ship with the fleet wide ship range a valuable asset.
On ships control of fighter and drone designs and even bombers being added to carriers would also be good. Also being able to upgrade the starting survey ship as better things get researched would be wonderful as well.