Many PC games have tried, few have succeeded to capture that supreme commander feeling without a lot of "Command and Conquer" style play which (IMHO) gets old rather quickly.
Medieval Total War is an excellent game. Years ago I played a few other Medieval style warfare games that were very good. But not too many modern war strategy games that I have played hit the mark.
Civilization IV looks good but I was a little disappointed with Civilization III so I am hesitant to buy it.
That's why I stick to games like SHIII, Warbirds 2005, and WWII online. being a pawn is more exciting (and dangerous) than being a general!