While there are some nasty issues in other areas, I love Dark Heresy/Rogue Trader's critical damage tables. 20 pages of truly entertaining ways of suffering severe injury, all based on the body part struck and method of damage. It's characterful, grimdark and funny all at the same time. The psychic tables in general for a similar atmospheric reason. I specialised in playing psykers and after experiencing how things can go wrong even when they go right, and the horrifying effects of the perils of the warp when it isn't being abstracted to 'take one wound', you better understand why everyone is scared of them.