First, get rid of the dumb puzzles used to open doors, and other hacks. They are not fun. You can’t figure a way to enhance your performance doing those puzzles. They are annoying and feel like imposed work instead of having fun.
Introduce a weaponless mode. At game start, the user should choose different characters, or buy different suits, allowing different game modes. A soldier should be able to use soldier weapons, but a hacker character/suit should not be able to use weapons, and should rely on stealth and traps.
A hacker should be able to hack firing turrets, plant bombs, military robots, remote controlling of doors (for example, forcing a door to close should kill a passing necromorph, and it should have collectable circuits allowing to automate a door trap).
A proximity explosive should destroy a panel liberating the killer gravity fields. Maybe a rope pasted (like the electric wires of bioshock) to the panel should remove the panel if a monster stumbles on the rope.
A rope in contact with an electric anomaly should turn into an electric wire trap. When wet, it should be deadlier.
Remote controlling surgical machines, lasers, and movable objects should work as traps, killing when automated with a commodity chip, or by manual player activation.
It should be possible to set stasis traps, and to combine traps. For example, a stasis trap near to a laser turret should stop a monster enough to be finished by the laser.
Traps should be used to cover the back, to avoid being attacked by surprise, or being flanked. It should be possible to spread flammable liquids, to be fired by traps, sparks (like a sparky door, or an electric switch), or falling of heavy objects.
You know than an air vent means monsters incoming. Put a trap on it.
The game should have some NPC (they don’t need to be human, so the isolation atmosphere is not broken) to be escorted to places which the NPC can hack in some way to get an advantage, for example, the NPC could be placed on a switch panel, so they activate traps when monsters pass over the traps, without requiring the player to manually controlling them, or spending circuits.
If the monsters kill the NPC, fighting the necros turns harder, and that adds a dimension to the game: how many NPCs can be escorted? That should require careful planning.
If the player is hurt enough by necromorphs, he should start losing his mind, turning to be controlled by the Marker, and he should sacrifice a NPC to recover his mind.
The player should choose, who to kill: a hacker? A scientist? A soldier?
NPCs should be able to get armor and upgrades, and the layer should choose between providing himself an armor, or give it to a vulnerable NPC.
Every dead body should be a danger, to be managed strategically. It could be turned into a necromorph, so the player should choose if destroying a body to eliminate a future enemy, or dragging the body to a hall, to be found by an enemy, who is distracted trying to resuscitate and transform the body, giving the player more time. Maybe dead bodies should be turnable into traps, like bombs, of virus that spread to nearby necromorphs.
Some necros should be attracted to dead bodies, and other should avoid them. That could be used to deviate a monster to a trap, like a door, or a killing surgical machine, or just to avoid weak necros to activate a trap destined to more powerful enemies.