Barotrauma

So far I have only played this one solo, though a group playthrough sounds like a fantastic idea to me. The learning curve was a bit rough - the apparent simplicity of the game led me to overlook things like order priority, etc... The move between biomes feels meaningful and impactful. Character builds and sub upgrades also feel significant. There is some enemy variety, though it essentially boils down to relatively small and trying to get into the sub, or really bug and just batting you around like a chewtoy. In the same vein, the missions are quite repetive. However where this game really shines is in its customisability. You have an in-game sub creator, and their code is available which has led to a flourishing mod community, who have injected a lot of variety into the game. The right combo of mods takes a good game and turns into a terrific game.

Run's at 5-30fps on average on my PC, sad