The very first Legendary weapon I found in Borderlands (it was like a level 15) and it just incinerated people. I used it forever. I was playing Lilith and it was perfect with her elemental skills.
In Borderlands 2, I LOVED the Hornet. It was a corrosive weapon with splash damage. You shoot one robot in a group and soon they're all melting. It was a burst fire weapon when zoomed. Robots are the main enemy in that game and it made them cake.
The Problem Solver in Fallout 4 is just a beast. Every hit on an enemy adds more and more damage. You mod it for automatic and nothing in the game can stand up to steady fire. It's so powerful that I don't use it unless I'm in a desperate situation.