The best RTS since WarCraft II
The graphics are colorful and varied, animations uniformly excellent, sound effects wonderful -- especially the female German villagers, and the cannons firing in quick succession. Multiplayer is really where this game shines.
The gameplay is extremely well-crafted and well-balanced. There's eight different nations, from the English, who breed like rabbits, to the Dutch, who accumulate vast wealth thanks to their bankers. All the nations are distinct from one another, and there's all sorts of play styles for different personalities. The Russians are for unpredictable wildcats, the Ottomans are for those who prefer blitzkrieg, and the Germans allow you to hire great numbers of powerful mercenaries. Of course if you want to hire ronin (masterless samurai) you'll have to go with Portugal.
One last thing: AoE3 uses the Havok physics middleware package, so when you blast apart a windmill you'll see individual beams of wood go flying. This also applies to humans: fire at a crowd of pikemen, and they'll be airbound in a no time. It's a very nice touch to this already spectacular game.
Single-player's only really value is to prepare you for multiplayer, and it doesn't do a very good job at that. Anyone who takes this game semi-seriously will make mincemeat out of you if your only experience is against the computer.
The storyline is instantly forgettable, but no worries, the developers surely developed this game with one thing in mind: massive multiplayer matches.
The Bottom Line
Pretty well a flawless game. Fortunately for me, I didn't waste my time on the previous installments of the Age of Empire series, nor any RTS since Warcraft 2, so when people tell you that AoE3 adds nothing new to the genre, they are both lying (Home Cities, for example) and suffering myopia from being too close to the genre. If you haven't played an RTS this is where you begin.