The overall area is pretty much circular with one "inaccessible" door, forcing the player to complete the area in a clockwise fashion. Reaching the area inaccessible via the main room is pretty much linear, with straight hallways and corridors. It is populated by aliens, support drones, and guardian drones. There are also a few opportunities for the player to sabotage turrets. Except for being a place where a unique version of shock baton can be found, the engine room is pretty similar to the rest of the ship, both in appearance and loot.
The area is composed of large main rooms, several small rooms, and hallways between them. It cannot be accessed after main quest is completed.
If you take Somah into the engine room she will make comments about smelling flammable gas as well as some vague comment about wondering 'what a well placed grenade would do to that thing'. Using a flamer does seem to ignite the flammable gas.
pc If exploring with noclip, there is a switch under the ground near the back of the level labeled "Release Control." In GECK it's labeled DLC05ERoomGasTrapControl and in the console it's labeled xx007a52.