The Europa Universalis series is great. Spent alot of time on 3 as England. Haven't had much play time on 4 yet. It's a very frustrating yet addictive and enjoyable experience.
The AI isn't just there to make up the numbers. They can be very very sneaky and underhanded. Got dragged into a Holy War in North Africa allied with Spain once, and just as I was about to take the last territory, claim the win and take Africa for myself, Spain negotiated a truce, where I got nothing except a winners medal. Before I could bring my troops home, Spain attacked France, which had been under English rule for 150 years and kicked me off mainland Europe.
I hate the Spanish.