The gameplay in Submarine Commander is quite similar to Faster Than Light (FTL), meaning you can only control your submarine through your crew. The main difference is, besides having extremely simple graphics, Submarine Commander is much more realistic and challenging.
Figuring out the controls in Submarine Commander is the main challenge of the game, since you can't use the mouse, and the keyboard controls are numerous and complicated. On the other hand, it's a roguelike, so if you're familiar with the genre, you're probably used to using complicated controls.
Once you've mastered the controls, you'll discover the game is huge and full of possibilities. You can fight other ships, travel the world, and try to survive dozens of unexpected situations that could possibly be the end for you and your crew.
Submarine Commander is an absolutely brilliant roguelike submarine simulator. Despite not having a particularly attractive graphics, it's a fun game and feels almost infinite in its content.