While new features, more provinces (especially your home country of course) are all great, in my opinion, one thing needs to be improved a lot, and a lot of resources should be devoted to it: The AI. With current computer power, I'm pretty sure a very good AI can be made, and this could become a great selling point for EU4 too. The primitiveness of the AI in EU3 is evident in modding, where one actually needs to write, eg. AI_will_do = 1 (not sure if that's the exact syntax), and then the AI will do it 100% certain if the conditions are met. A better AI would just look at an event, and evaluate its usefulness, etc. Multiplayer is great, but in such a grand strategy game, the AI is even essential in Multiplayer games.
