My first Tough game, 9 civs, large map.
After I conquered one of them I already got good technological edge.
So just for the fun I started gifing techs, but to my suprise, several techs where enough to buy alliane from all civs and achive diplomatic vicroty. Was a bit harder against Drengin (needed more techs), since I was human, but not that much.
So that's how I got my very unfullfilling diplomacy victory.
Good tech advantage means auto-win.
.
Anyway, I guess Stardock coders need lot to learn from Civilization games, since I noticed some old exploits I used in reduced form in Civ3 (not in Civ4) still live in kicking at much higher intensity.
"Tech whoring", when player trades techs between aliens that they didn't traded themself. It's very easy this way to get tech edge (Civ3 solved it, in pacthes, by AI agressive trading, Civ4 by both smart AI trading and restricted trading of new AI discovered techs).
Also, AI values sudden giftes in diplomacy a lot, which means that showering AI in gifts is easy way to get what you want. It should be longer process. Diplomacy modifier for gifts per turn should be capped, to promote longer diplomacy acitvity. Gifts over time should be encouraged.