The "catch" to Empire Earth
was that you played as one civilization through multiple eras. You began in ancient times and worked your way up through time periods, ending up in a robot dominated future. The original system was a great one and worked fine, which makes you wonder why anyone bothered to change it. Originally you have over a dozen eras to work through; now you have five and it doesn't take too long to get through them all. This removes most, if not all, of the game's charm and strategy, regaling it to just another RTS.
Another cutback involves the various factions. Empire Earth III gives you three: West, East and Middle East. Each features the stock traits found in all RTS factions. The West is a military powerhouse with expensive, but effective units, while the East has the numbers with its cheap, expendable units. The difference between the factions is noticeable early on, though later it really won't matter much. Again, this pulls away what made the series unique and places it in a category that can only be referred to as generic.
Not all of the changes are bad; in the process of scaling back everything, some of the elements that needed to be changed were. Chief among these is the economic model, which has been broken down into two manageable categories: Wealth and Materials. The latter can be obtained from any resource pile on the map while the former is produced through trading. One really neat aspect of wealth is the risk/ reward element; the further you send your traders, the more wealth you'll gain. However, sending them too far out also leaves them open to attack, leaving you with the decision to play it safe, or risk financial stability in the hope of bigger profits.
The single-player campaign is a turn-based battle for control of the world. The premise is sort of like Risk, where you lead your armies into different areas of the map. The more territories you control, the more resources you have. If a territory is under another faction's control, you'll have to fight them; if it isn't, you'll have to square off with the natives. At certain points in the campaign you may have to complete special events, such as defending a territory from barbarians.
Overall, the mode works great, though the logic doesn't always make sense. Some of the scenarios that pop up come from left field, which hurts the overall experience. The entire mode could benefit from some sort of structure. There's little motivation to keep conquering other territories other than playing the game. Objectives aren't very interesting, nor are you given many options. For example, diplomatic options are limited to war and alliance; a little more complexity, or at least more choices, would have been welcome. Compare this to Rise of Nations or Dark Crusade where decisions feel a little more meaningful.