Pffft, that's a bad DM. What he should do is let you roll all your dice, and then the more you overkill it, the more he describes it as some horrible mutilation. You overkill a goblin by 50 with a sneak attack? Sound like what you did was grabbed the goblin by the back of the neck, and lifted it off the ground, repeatedly stabbing it in the back, while it kicks and flails screaming helplessly against your onslaught. You only stop when its diced innards are literally falling out the wretched creatures back, dropping its body to the floor and pointing at one of the other goblins, make an intimidation check.
Boom, now your a badass instead of feeling trashy.