Original subterrain is very fun and interesting game. I play it about 10 times and got bored.
It is not famous like doom because it does not have mod support. If there is no mod support, we need remake or remastered of this game. This game should have....
1. New game plus to unlock
1.1 New weapons.
1.2 New armor.
1.3 Hybrid weapon and armor crafting system and modding status or attributes.
1.4 New items like foods, drinks and boost items.
1.5 New monsters or mutation monsters.
1.6 New planets
2. Mini-boss
3. New places or maps
4. Secrets
5. More armor slots like helmet, armor, hands, arms, greaves, boots in order to boost or upgrade. like night vision goggles on helmet or boost speed on boots or greaves or boost reload speed on arms.
6. Side quests. like save survivors to boost work time for players at mining or researching or farming or crafting or repairing.
7. Alternate main quest option.
8. More ending option upon side quests and main quests leading to new planet
9. New tower defense quest at other places like defense reactors.
10. Leveling system and skills.

If there are all this option, this game can be sold again.