I have two campaigns at the same time, one solo, one with a friend. I am amazed how different the campaigns are. Moreover, by discussing with my other friends that play the game, I could play two or three more campaigns and there will be significant differences between the four of them. Per exemple, I have not played dark urge, broken oath paladin, no evil run (I have one but I wasn't evil enough). The replayability is surprisingly good.

I have not finished the game. I'm in Act 3 in one of the campaigns. One thing that help make the campaigns differents is to do the quests in different orders. It lead to unexpected changes.