Hiya!
Full Disclosure: I fully admit to being what is considered a "Killer DM" in todays, uh, hmmm....don't know how to put it, so I'll just be blunt: "I'm a Killer DM when compared to a surprising amount of more modern DM's where coddling the players and their characters is preferred to letting them die and change the story/plot". (e.g., DM's that actively try to avoid killing PC's).
Yup. Killer DM.

And dang proud of it too! My players KNOW that I don't pull punches or otherwise favour their PC's. If they want to survive, they have to be smart, cautious, and work together. Alas, my players also have an (as of yet) incurable case of individually-created-PC's-without-consult-to-other-players. Meaning they don't tend to create characters as "a group" (a problem they learned in the 3e days), and thus end up with a Fighter, Barbarian, Fighter, Thief....or Warlock, Wizard, Bard, Sorcerer...or Cleric, Thief, Bard, Thief....you get the point. So when they get to that heavily locked/trapped door, or that impassible stone block, or magical force-field, well, they're screwed. Not my fault. When they DO work together and create complementary PC's (which, I am happy to report, they have been doing
ever so slight more over the last half year or so), they do MUCH better. That's how they managed to get the Barbarian to 7th, Druid to 5th, and Thief to 4th; they were all in the same 'adventuring party' (I think the Warlock got to 3rd).
Anyway, yeah. I am "adversarial" in that I am playing the parts of the monsters, NPC's and environment. I "want" to kill/capture the PC's in as much as I'm the 'bad guys'. I mean, if I was one of those "old skool Killer DM's", well, the old quote of "Rocks fall. Everyone dies" didn't just come out of no-where. Any DM can "kill PC's"...its being able to do that and have your players coming back for more that tells you you're doing it "right".
^_^
Paul L. Ming