Okay, I spent some time int he game, however not very much. I'm currently at day 2.
So far I can say the game is very deep and complex. This does not automatically mean that a game is good but it suits this game very well and it was very well integrated into the gameplay.
Basically it's a looting game, you plan where you want to go, loot areas of the colony and return back to your base with materials and garbage items that you can recycle. Between your expiditions you invest time in researching items you found which unlocks new crafting recipes or you recycle your garbage or unwanted items, craft from the ganied materials some new equipment. You can improve literally everything, your weapons, your inventory, the energy reactor, buildings in the game. It's really crazy how much you can improve here. There is always soemthign to do that keeps the player enganged and entertained.
There are two main resources in the game, energy and time. Energy can be distributed to the different areas of the colony when you are at your base. At the beginning you have enough energy to maintain everything you need, but the reacter degenerates over time and it gets even worse if you get attacked. You can craft better reactor modules from materials at some point which gives you more energy and allow you to power up more areas at the same time.
If you don't find garbage to recycle, you can also extract ore fromt he nearby mine or grow some plants in the biosphere.
The survival aspect fromt he game comes from two different sources. First are your needs. This turns out to be exactly like in "The Sims". You need food, sleep, drinking and even go to the toilet. Additionally you have also to keep the infection low, that is spreading inside of you.
The other obvious source are of course the enemies. They seem to be some zombie-like mutants in different categories. The map gives you an indication with the infection rate, how many enemies are in that area. If you kill an enemy, the rate drops, over time the rate will increase and so will the enemy activity. You can decrease the speed at which the rate grows if you power up an area and have functioning oxygen and temperature regulators. The infection spreads quick on areas with low oxygen and temperature levels.
eventually enemies will attack your base and focus on the reactor. If the reactor gets destroyed, you will loose (no power=no oxygen). You can insert weapons you find in turret slots and the turrets will then take the weapon and fire with it on incoming enemies. This has soem very slight tower defense value, however, turrets are at fixed places and you can only equip them with one type of weapons, SMGs. It would be cooler if you could equip the other weapon types (except melee) as well.
The game reminds me like a mix of Ghost of Mars, Last Days on Mars (both films feature a similiar scenario), the Dead Space series (especially DS2 which plays also on some kind of colony) and Take on Mars (the Mars colonization mode to be precise).
Subterrain feels very well developed and has a very nice and scary atmophere which you get rarely in a top-down horror game. I do find the enemies at this point a little too easy to kill. This may change in the latter parts of the game however.
