The curse of the real time

Most likely due to requirements of the multiplayer support, EU3 is a game that should have been turn based, but instead it was forced to the mold of a real time game. You can issue orders while paused, so in practice the gameplay is pretty close to a turn-based experience. You set your orders - build a new army here, construct a new building there, send this fleet some place - and then unpause the game and watch the days go by until something happens, or until your units are done with their tasks. A major missing feature is "pause on an event" which would automatically pause the game when something interesting happens. In any case, a big portion of the early gameplay is spent alternating between fast forwarding in time and pausing the game.

Luckily you'll get used to fiddling with the time settings and as a flipside to this, being a real time game allows Europa Universalis III to support proper multiplayer for up to 32 people. You can either play on LAN, or via online matchmaking system (which requires you to register your copy of the game). There is also something new and innovative in the multiplayer - you can also play with your friend as cooperative rulers of a single country against other players or the computer.

Diplomacy and the stuff that happens when it fails

One side where Europa Universalis III shines is its diplomacy system. Some people call diplomacy the "art of getting the other guys to fight each other instead of you" and this definitely applies here. By carefully maneuvering your relations with arranged marriages, alliances and a healthy bribe or two, you can concentrate on more peaceful goals such as colonization and trade. You could end up with the rest of the Europe being tied up in beating each other senseless, while you happily spend your resources in technological development and strengthening your defenses. Diplomatic options also include such moves as subsidizing other countries wars and influencing revolts through espionage.

And when diplomacy fails, even then there is a diplomatic protocol to adhere to. Nations generally need a Casius Belli (a reason for war) before they can start bashing their enemies to a pulp, or they risk an internal uprising from their own population. Shrewd diplomats can manufacture a good enough reason, entice their opponents to fire the first shot, and then respond (with a natural Casius Belli, as your enemies shot first) with a well planned assault.

You can also take over other nations through diplomatic means. You can build great relations to a nation and then ask them to become your vassals, providing half of their tax income to you, and then later move to fully annex the smaller nation without firing a single shot. Or you can beat the other nation up until they agree to annexation either at gunpoint or via diplomatic talks. However, all actions affect your reputation, and leaders heading for global conquest tend to run into problems as nobody will trust you any longer. Best bet is to use military force only when needed, and to carefully choose your allies, as no nation can take on the rest of the world alone.