The most important new feature to add would be a decent editor like the previous version had.
Dragon Emperor
If the AI behaved intelligently a strategy game could get by fine without multiplayer. However, every single player strategy game I have ever played suffers from the same AI problems. The AIs cannot react intelligently to your actions the way real people can (well, some people). For example: 1) Computers have no concept of territorial claims, and thus can provoke war by grabbing something from a strong player that a human would know not to.
Ever since I applied the latest patch the game has been periodically choosing turns to crash on. The only way to continue is to load an older save and try to get it to be different enough to continue. It is getting very annoying and until the bug gets fixed there is no point in playing any more. I am using the latest GalCiv: Altarian Prophecy.