I think I remember you asking, and that you were less than impressed witch Shadowdark. Honestly, I am kinda surprised you still read about it, from what I recall of that thread. Maybe I misremember, though.
Regarding the complexity, I reckon it would be quite fickle. Easy to do, but easy to go to far. That's very subjective to my preference, to be clear! I just want to point out the value of simplicity, as in no complexity for complexities’ sake.
Coming from 5e, lethality is the obvious one. It is often overstated, but obviously differs from table to table. For me, the main point is simple OSR stuff, like player skill over character skill. To me, pretty much, I run it much like 5e, but the characters are no superheroes. Probably, my 5e tables lean rather OSR, if that makes sense.
Honestly, you only need the free quick starter to get gong. The core book, in my opinion, could last you a lifetime. You do NOT need anything more ruleswise. That said, I think all the rest is amazing value. I do not know where else you can get a better deal.