System shock is an interesting idea for someone who comes to Advanced Dungeons and Dragons Second Edition (AD&D 2e) from a Dungeons & Dragons Third Edition (D&D 3e) perspective. The basic idea of system shock is that sometimes the body goes through some act that is so traumatic that the shock to the system could cause instant death. This can include magical effects that reshape the body, that cause advanced aging, and similar effects.
This didn’t exist when I began playing.
D&D 3e would begin the transition away from instant death effects by getting rid of system shock and largely moving away from instant kill spells (though they still existed). The argument that I have seen online is that players didn’t want instant death effects in the game anymore and so designers moved in that direction; however, the idea that you would need to roll to survive extreme events to your body is a sensible one and I find it highly appealing.
Dragons Never Forget 
System Shock survival is one of those little micro-systems in AD&D that I liked. Though it didn’t come up very often, it made sense. Further, it didn’t have a “ripple effect” into the other parts of the game. It’s kinda hard to compare System Shock with Fortitude Save, but the former is at lot less complex than the latter.
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Agreed.
The other thing that I like about System Shock is that it doesn’t feel like you’re trying to power through the save. Like with Fortitude, okay, there comes a point where it becomes practically impossible to fail and if you build your character in a certain way then that comes earlier in the game. With AD&D 2e that point comes from the start. If your ability score is high enough, congratulations. You’re not going to fail this but 1% of the time.
I like that. A lot
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