Something I'd like to see (and even love if it was applied to existing content)--when you run across a door that only unlocks when mobs are killed, there's a glowing aura on the door/lever/whatever that says "lifeseal" if you click on it, and the mobs you have to kill have a similar glow.
It would communicate what you have to do, and would also be less lame than a door that somehow knows to unlock itself when the last hobgoblin dies.