Like that dark change mid way!

Superb GD tune!

Great composition. lots of cool hooks. As far as it sounding modern, and if that is a problem even - then export in mono for instant retro.The effect is dramatic, instant old skool - give it a try.
If being in Mono really bothers you, then I'd suggest using much less reverb or using more crunchy, less sophisticated verbs such as oil drum or spring. The impression I get is that its clean sounding - not a negative at all, but old 16bit machines or 8bit would either not have the capacity for reverb, or would have very lo res versions of verb.