Played SE IV long ago, and considering SE V.

[Raapys]

I don't know, I think there are few direct improvements over SEIV, and none of them major. And there are many dubious changes, and some that are simply bad( like the UI ). Stuff like the new "3D" combat system wont even be noticed much if you play simultaneous mode or multiplayer. The turn processing times are much longer than SEIV's, making single-player a chore. Some of the new game features cripples the AI so that it becomes even worse than in SEIV.

On the bright side, the modding capabilities of the game have been improved greatly.

To sum it up for my own part, had SEIV had the same modding capabilities and the continued patch support from the developer then I'd see no reason at all to go for SEV; SEIV is simply a better game in most areas. As it is though, SEV has both these things and is thus slowly improving.