I've played two 2-player games, both seemed fairly balanced, and ended with a very close race to victory. We desided to play with infinite old world cards, as we didn't want to stop the game just because we ran out, but we could have played with either 7 or 8, as both games ended around here.
First game was Khorne vs. Nurgle, and we figured Khorne would have a major advantage because his dial advancement was focused on killing the other player. It turned out quite intense, with both gods winning double dials at different times, and it ended with a very unexpected victory for Nurgle. he needed 1 dial advancement to win, and Khorne needed two with the most VP, and the round ended with combat in 4 regions, with Nurgle getting only one populus, but as luck would have it Khorne only killed in one, so Nurgle won. Khorne ended up having a hard time killing since there was only one players figures, and he always rand out of power first, so getting combat in multiple regions wasn't easy.
The second game was Slaanesh vs. Tzeentch, which naturally played out with alot less combat, and much more focus on dials, this also ended with a very close race at the end, with Slaanesh taking the lead, since he had 9 power, and was lucky that Tzeentch didn't have many 0-cards, so he got the last rounds, otherwice Tzeentch could just have moved his cultists with warpstones arbitrarily to safety and won.
Both games feelt fairly balanced, and were quite amusing, nothing like a 4 player game, but ok.