'The Mythos', as a codified structure, is Derleth's idea. Lovecraft's work is better appreciated outside that conception.
There are lots of good writers with Lovecraft elements in their work, including Robert Bloch, Hugh B. Cave, Robert E. Howard, Clark Ashton Smith, A.A. Attanasio, Jorge Luis Borges (try 'There Are More Things'), Ramsey Campbell, Caitlín R. Kiernan, T.E.D. Klein, Thomas Ligotti, Mark Samuels, and Karl Edward Wagner.
There are lots of good writers with Lovecraft elements in their work, including Robert Bloch, Hugh B. Cave, Robert E. Howard, Clark Ashton Smith, A.A. Attanasio, Jorge Luis Borges (try 'There Are More Things'), Ramsey Campbell, Caitlín R. Kiernan, T.E.D. Klein, Thomas Ligotti, Mark Samuels, and Karl Edward Wagner.