Clumsy, boring, tedious
First, the interface is good on ideas lousy on execution. The picture in picture idea is interesting, but in practice feels more like a gimmick. No value. Second, there are various levels of overview maps that are supposed to help manage resource harvesting. Moderately helpful, but totally useless when you are waging war at the same time because (this takes us to point number three) the unit command, control, pop cap and AI are all terrible. Some of the worst I have seen in a highly touted game release.
Also, the tech tree feels like it's not really even integrated into the game (you research tech to provide unit and building bonuses). Battles quickly break down into mad scrambles. Unit production takes an amazingly long time and population caps are set at fairly low levels. Buildings don't feel like they are assisting your civization to advance and you will constantly find yourself needing to put more citizens inside of the buildings to get them to actually do anything once you build them. You will constantly be asking yourself, "gee, should I build up my army to stop the conquering hordes from overwhelming or do I build another 10 citizens so that I can generate additional research points?" Conquering enemy territory feels like RTS armies gone wild...you don't really need nor can you accomplish much strategy. About all you can do is produce a many units as you can and then send them headlong into battle.
If you must spend money on an Empire Earth game, get the first one out of the bargain bin. There are too many other good RTS games out there to waste any of your gaming time or money on this mess.