Steam Marines will definitely appeal to a small subset of people, but not to a general gamer audience and certainly not to me (and I love roguelikes!).
To not die within the first couple of floors of Steam Marine, you must play extremely cautiously. Open a door; set up the rest of the squad to guard behind. Look around the room; set up the rest of the squad to guard. If there are enemies, kite backwards while setting the rest of the squad to guard and maybe get some pot shots in. Failure to do any of these things risks the chance of some ranged bot popping out the shadows and taking a marine from full health to dead/near dead in a single turn. You have a rough idea of where enemies are from hearing their footsteps, but you have no idea how the rooms and doors are connected until you actually pop your head in and turn about.
The marine health/enemy damage ratio is so very low, so there is no room for error. Trying to run and gun, or even advance to a forward position and burst an enemy down, will get you killed very fast.
This demanded precision is frustrated by the control scheme: every of the many actions has a mapped key, with NO context sensitivity. While I'm used to games like this, the learning curve is still a little steep, and the memorization will be a turn-off for many people. This frustration is compounded by the fact that there is no undo, even for benign actions with no impact on the immediate turn, such as guarding. Did you just hit the wrong key at a critical turn and accidentally fire at nothing, or guard into a wall, or use an item you didn’t intend to, etc.? All your hours and effort is wasted now, your run is over.
If a repetitive, boring, and cautious slog through a hardcore dungeon where small mistakes will waste hours of work sounds exciting to you, this game is for you. Again, I’m sure there are some people who will enjoy such a neurotic challenge, but this experience is not for most.