I've recently been looking at older stories to gauge how bloodthirsty a lot of the villains can be. Spidey's rogue gallery has always been my favorite set of villains since they were always shown to be quite unique in their ways.
-Some were just criminals that only cared about power and wealth (Shocker, Mysterio, Hobgoblin, Vulture, Electro, etc)
-Some were just criminals that had no direction, but weren't really bad (Sandman)
-Some were psychotic and enjoyed killing to prove a point or for fun (Carnage, Doc Ock, Green Goblin, etc)
-Some only cared about revenge (Venom)
-Some started out seeking revenge only to take it further (Scorpion, Smythe
-Some did it for sport (Kraven)
In Marvel Knights, there was a scene where Electro was so mad about losing $20 million that he blew up all of the cars (that had people in them) that were in the area. This was surprising to me because Electro always seemed like one of those guys who'd never go that far. Well, not literally. There was a story where Electro made Spidey beg for his life or he was going to destroy the closest neighborhoods with his new powers. That seemed to be an ego thing, though.
Vulture is one of the characters that seemed to get darker as the stories continued. Toomes was always a criminal, but Spectacular #186-188 seemed to turn him into a remorseless killer. The only time where he appeared to have remorse was when Nathan died because of his antics, since it was an accident. He totally accepted his responsibility in the matter and asked for May's forgiveness, but his brutality remained. He even goes straight to the Daily Bugle and threatens to kill Jameson if he doesn't change the headline to the paper. Most of this seemed to build-up from his various defeats at the hands of Spidey over the yrs.
This page does a great job in in highlighting Vulture's cold-blooded nature
and the tragic circumstances surrounding him:
You can't help but feel sorry for him when reading that. This is easily the best Vulture story imo.
Doc Ock is another one of those who've hatched countless plans to wipe out NYC to prove his superiority or just to kill Spidey. He was fine with poisoning the water supply in NYC, destroying the city with the neuron bomb during the Owl Gang War, releasing a germ to kill Spidey because he was too traumatized by him, the stuff he did with the electronics in #600, and the Ends of the Earth.
So when it comes to brutal nature of Spidey's villains, which ones stand out to you the most?