I fondly recall the sim games of the late eighties/early nineties. Alongside Will Wright's brilliant contributions was Aerobiz and Aerobiz: Supersonic, both featuring great music, challenging campaigns and, most importantly, fun and addictive simulation. Aerobiz placed you in charge of your own airline; you were to manage and operate your airline from opening routes to buying planes to micromanaging your ticket prices. Though it may not have been as encompassing as similar games like SimCity, Aerobiz offered tonnes of fun and replayibility.
Did I mention that there was 4-player competitive multiplayer?