An excellent Paradox game, with one of the fastest learning curve and a lot of depth if given time.
The best part is the online community, based upon the Paradox forums. Any question you may have will be answered there. The multiplayer is a very interesting aspect, with many games being played each month (even though you may have some stablity problems if one of the players have a slow PC).
Finally you have a very wide selection of MODs made by the users, which enhance the game to unexpected levels of fun and challenge. The mods are easy to download and you can have a lot of them installed at the same time. Even YOU can mod the game, changing taxes, population or leaders names, like I did.