Awesomeness generally occurs on the seldom occasions that a Lovecraft work goes without a crapsack ending. The first example that comes to mind is the end of The Call of Cthulhu, in which the remaining group of sailors, in an attempt to drive the horror that they unleashed back into the sea, slam into Cthulhu's face with a cruise ship, thus trapping him in R'lyeh once more.
When Lovecraft kills his creatures, he tends to kill them hard. The Shunned House features an altercation with a buried, immobile and gargantuan monster that is haunting a house by projecting its miasmal essence through the crook in its elbow, which is just below the basement. After said miasma kills the main character's uncle in an admittedly nightmarish way, the main character decides to strike back by pouring several barrels of acid on the monster until it dies screaming. This not only kills it, but allows the terrible stigma that's affected the house for so long to finally lift.
Also of note from that story is the protagonist and his uncle's weapons of choice for the stakeout of the house's basement. In a surprising case of Crazy-Prepared, he and his uncle order two sets of defensive measures in the event the thing in the basement is solid or incorporeal: if incorporeal, they had prepared some sort of precursor to the Ghostbusters apparatus, and if corporeal, they had a pair of World War I-era flamethrowers.
The end of The Dunwich Horror, in which our protagonists blow up a spawn of Yog-Sothoth with dynamite.
The Colour Out of Space where Lovecraft is able to make a goddamned color scary.
In The Case of Charles Dexter Ward, Dr. Willett manages to beat Curwen at his own game.