Developers didn't focus on super graphics (although, to be fair, the graphics in all the games mentioned were quite decent for that time). Instead, they focused on creating an atmosphere through gameplay, plot, video cutscenes, and, importantly, sound design. Can any of us say that we haven't hummed tunes from 90s games? I still have compositions from C&C (on the prowl), Crusader (main theme, resistance), and Heroes 2 (battle 1, 2, 3, rampart) on my phone.
I'll digress a bit. Modern developers seem to be losing their way due to the abundance of modern graphical capabilities. Everyone has forgotten about gameplay, atmosphere, and high-quality sound design.
But there are companies like Firaxis. They deserve praise. They made a very successful attempt to revive XCOM, and they succeeded. Why? Because the old Sid said that their company sacrificed, for example, high-quality multiplayer and graphics in favor of a high-quality single-player experience.