Basically, Fantasy Wars (and Elven Legacy) are modern versions of SSI's classic Fantasy General. If you haven't played that, then imagine Panzer General in a fantasy setting. If you still have no idea, then... hm, well, I guess it could be described more complex fantasy-version of Battle Isle/Massive Assault.
Gah, it's hard when almost all the games I know this game is similar to are ancient. We need more turn-based strategy games, dammit.