For more than 5 years, I still love this game.
Personally, this game has been part of my childhood and I remember sneaking out late at night to turn on the computer to to play it ( yes, I'm Asian and my parents want me to study hard). To me, AOE 3 offered a dream-like graphic and homey atmosphere especially if you have a good graphic card to enable the highest shader. The maps have a lot of details and many little things like treasures or native tribes to play around.
About the game play, this game is more straightfoward. You will find your army cluster in close organized formations which makes the fighting really like skirmishes instead of huge battles. Cannons shooting from behind, followed by ranged units and hand units take the leading charges. The fun of it is to command different types of units separately eg to make your cavalries sneak from behind hostile armies and take out the cannons. Sea battles are less flexible as the war ships are rather slow but there is a lot of room for surprise elements if you can take the sea routes to transport your army at the enemies' backyard.
The AIs are pretty smart in this game. No more units being stuck in the middle of the jungles nor they being oblivious to enemy units near them. Your allies will help you very often and are very responsive to your commands.
You can improve the game experience if you apply certain mods. I recommend changing your Settler's population count in the file 'Proto' in "data' folder to 0 to allow larger armies( and similarly reduce your unique unit's population count if you want to reign over your enemies with larger number later). Apply the Improvement mod will improve the AI SIGNIFICANTLY because they are can change their unit types to respond to your units and they can build Fort Wall surround their cities !!!.
So don't miss this classic game, buy it and have fun