This game is a dear favorite of mine, in part because I am a student of historical anthropology and warfare. As such, this game might as well have been made for me!
Empire Earth is a strategy game somewhere between Warcraft and Civilization in structure, where you harvest resources (including hunting/gathering!) and attempt to build a civilization. The point of the game is either to win militarily or by constructing a set amount (typically 3) of "wonders" such as the library of Alexandria.
What makes EE so epic in scope is the fact that you are constantly progressing through various "epochs" of development...so you might start with cavemen, and end with Napoleonic soldiers, or futuristic cyber men! This aspect of the game, particularly if you play through multiple epochs in one game, really illustrates the depth of the engine. The nuances of the game drastically change as you progress, as new technologies make older strategies and defenses obsolete. The first time I had to face aircraft was...interesting to say the least.
Empire Earth is one of my favorite strategy titles of all time, and it sits right up top with Civilization and Total War in my opinion.