The top 10 Lovecraft stories can vary depending on personal preferences, but some commonly mentioned ones are 'The Call of Cthulhu' for its iconic cosmic horror, 'At the Mountains of Madness' with its exploration themes, 'The Dunwich Horror' for its creepy rural setting, 'The Shadow over Innsmouth' for its fishy mysteries, 'The Colour out of Space' for its strange phenomenon, 'The Whisperer in Darkness' for its alien elements, 'The Rats in the Walls' for its ancestral horror, 'The Haunter of the Dark' for its dark cults, 'The Thing on the Doorstep' for its body-swapping horror, and 'Pickman's Model' for its artistic terror.
Not all Lovecraft stories are in the public domain. The determination depends on factors like the year of publication and whether copyright was renewed. It's best to research each story individually to know for sure.
Among Lovecraft's works, 'The Shadow Out of Time' could be seen as a sequel of sorts. It expands on the ideas of ancient and otherworldly influences. These sequels often share common themes and motifs across his body of work.
I think 'The Rats in the Walls' is among the best. It follows a man who returns to his ancestral home only to be haunted by the sounds of rats in the walls. It turns out there are far more sinister things going on. Also, 'Pickman's Model' is a great story. It features an artist who creates disturbing paintings that seem to be more than just art, but glimpses into a nightmarish underworld.