If you've played Empire Earth 2 to the core, you'll find most of Art of Supremacy to be a bit repetitive.
1. Gameplay - No major changes here. However I would like to mention the newly introduced factions and gameplay modes. 4 new factions are introduced - Masai, Zulu, French and the Russians (Yes the French and the Russians were skipped in the original game so that they could include it in here). This is garnished by a new Egyptian campaign and a Napoleonic War, thought I feel that the latter is too overused to be included in a modern RTS game. A new gameplay mode is the Tug - Of - War which pits 2 warring nations over a series of battles and a multitude of home lands to invade (or defend, as the case may be). You can compare this gameplay mode to the Conquer the World campaign in Rise of Nations. Moreover, much like in Age of Empires III, you'll find tribal villages such as the Iroquis or the Olmec. Though it adds a lot to the gameplay experience, it can hardly but remove the redundant feeling of the game. Certain stuffs like Warrior Spirit and something with fertility has also been added, but I didn't find the right mentality to check them out. I found them pretty trite.
2. Music and graphics haven't been improved much in this game expansion.
The final verdict on this game is that unless you're an avid Empire Earth 2 fan (like me :D ), you might want to hold back on your purse.