Brilliant game, if it works well. And with me, it works well.
Now, onto the actual game. The Grand Campaign is incredibly deep, you might even call it a grand strategy game. It's not on the level of a game such as Europa Universalis, but its not far off. Prepare to manage taxes for both nobility and commoners, to raid trade routes and fight pirates.
One of the main 'back of the box' features of this game is the naval battles, which are fantastic. It takes a little getting used to, as the bigger ships are quite cumbersome, but there is infinite satisfaction to be had boarding, sinking or even blowing up other ships.
The graphics are incredible. With my PC (see above, or blog for specs) I can afford to run the game with everything set to Ultra and with 4xAA and 16xAF without a hitch. That said, I do like to turn down the AA a bit for the big naval battles, as they are quite a handful. However, if you are the owner of a more modest PC, even medium and low settings still look reasonably nice. However, if you are the owner of a computer which only just scrapes the minimum requirements, do not buy this game. The minimum requirements are a scam!
Replayability is basically endless. The grand campaign is so large, and there are so many factions to play as that no play through will be the same. Even if you play as the same faction you did last time, it will be different.