Between the "special worlds" and "custom opponents", I'm already sold. The rest is just icing. The interview on Gamespot was interesting, too.
There are things that haven't been mentioned yet that I think would also make great additions. Think of this as a "request list". (Of course, I've already confessed that I'll buy the expansion anyway, but still.)
Fixing a trade exploit. Right now, if you offer, say, Laser 3 and 4 in the same deal, the AI will complain. But it'll take them
separately - if you sell it Laser 3 and THEN 4 in the same turn, it'll pay for both. It should be able to see what's going on there.
Heroes. This is what I voted for in the "what do you want most in an sequel" poll, and luckily, the developers seem to want it, too. I can only hope they change their minds and try it for the expansion pack.
Some explanation for why the Dread Lords never got a tech victory. It always seemed silly to me that the Dread Lords are this hyper-advanced race who have been hyper-advanced for aeons and are still here, but the main races (whose tech is vastly inferior) can win a tech victory and "transcend mortality" after only a few in-game years. Seems like kind of a plot hole to me. Maybe the Dread Lords are like the Overlords in Clarke's "Childhood's End", badass but lacking the godlike potential of the seemingly inferior races (that might help explain why the Dread Lords wanted to wipe out all the upstart evolving races in the beginning). Then again, maybe transcendence would explain why the Dread Lords' weapon/soldier bonuses are so obscene. This is definitely an issue I'd like to see more about, Stardock could probably come up with a really interesting answer here.
A more voluntary UP. I'm not really happy with the UP issues in GalCiv 2...it's too random and inflexible to be much use. There are issues that could really help or screw you, but - even though you have plenty of warning that a vote is coming - you don't know which issue will come up. I never buy "influence points" the AI. It sucks to buy them and then have the issue be something I don't care about.
I've always felt the UP issues should be more like the UN stuff in Alpha Centauri...in that game, anyone could call for votes on issues (planetary governor, lift atrocity prohibitions, salvage Unity core, etc) at any time, although no faction could call more than one vote a turn or whatever. And on the voting screen, you could click on the AI factions and go right into diplomacy to bribe them into changing their vote, if it was an issue they were willing to bend on. It would be nice if GalCiv 2 also offered this flexibility. Admittedly, it would change the game dynamics quite a bit. For example, evil races would probably become even more aggressive in their expansion, trying to ensure they'll have the influence to defeat the inevitable "reduced trade routes if you're evil" law that good races will try to hammer them with. It'd also make militarily weak but strong influence races more dangerous and viale. Sure, you could kick their ass in a war, but are you going to do it if they could pass a bunch of resolutions that would make things harder for you for the rest of the game?
More alignment-related things you can do. I've speculated/bitched about this point more than once on this forum, but I'll never tire of it. It'd be nice if your alignment shifted towards evil for starting wars (at least against good races). Even better would be empire-wide policies or something I could do to show my alignment, like slavery (production boost) or repressive government (loyalty boost) if I'm evil, or poor/disaster relief (morale boost, but constant cost) if I'm good.