Game-Breaker: To compensate for the fact that you don't have any other projectile weapons, the taser gun you get for the duration of the mining area will render anything it hits incapable of movement for several seconds, ready to be boot-stomped into the afterlife. In the original 2004 release, it can even stun the exoskeleton guards for a few seconds.
Nightmare Fuel: After falling into the Pit, you first have to find a way with only a few minutes of battery left in your torch, and a little later you have another task to do there with just a dozen flares at disposal. All this while natural light sources are almost nil (you don't have the Eyeshine yet), and with constant assaults by small packs of Dwellers - men thrown down there and devolved into a feral state by madness and exposure to toxic waste. The alien beasts you encounter later can be unsettling, but never like that thankfully short level.
Polished Port: The second PC version has updated visuals, gameplay improvements, and the added content of the first PC version. On top of that, it comes free with it's sequel.