In My Opinion, This game dwarves the civ series in terms of strategy and options for your empire. This removes the sometimes annoying turn based Campaigns of Civ and total war with a somewhat hybrid of Rts and the option for you to manually turn base the game.
The not only big but HUGE map make the Civ and Total war map, which are but a fraction of the size, look like mere concepts for EU3.
The online play on EU is also one of the best in this kind of game that i have played, you dont need to sit around waiting while your team-mate finishes their turn while you are, for example, waiting for a tech level. Me and my friends loved splitting the map into sections and setting goals for conquest.
The game-play itself is Insanely deep, one thing that we loved, when comparing to Total war and the Civ series, was the Suing for peace options, instead of simply taking provinces from the enemy state, instead you will need to damage the nation as much as possible in various ways to either cede provinces, revoke the enemies claim on provinces, force them to release nations from their control, or even annex the nation completely.
Another point that i found so much better than the total war series, was the ability to create vassals from your states or from enemy states, i found this alot more useful and more of an intriguing function than that of protectorates within Empire total war for example, as you would have to have their entire nation surrounded and still pay an obscene amount of money or other tributes to make this happen.
One of my personal favorite features of this game was the ability to play around with the Holy Roman Empire. This opens up many different historical paths for the payer to take. I formed the holy roman empire into a single state, then Occupied all of Europe to create a catholic super state, however, on another save have completely dismantled the HRE, following the Napoleonic path.
All in all, this is an amazingly deep game, that cannot be truly judged until you have fully gotten into it, i understand that this may not be for some players as to being with the gameplay is slow and somewhat confusing, but after this, when about 30-35 years in you get the idea and will either decide that it isnt for you, or that this is the game that youve been waiting for..... 10/10, best game in years