Ramsey Campbell has five basic periods:

1. Lovecraftian short fiction in the first half of the 1970's, which gradually morphs into paranoid atmospherics set in then-contemporary urban England
2. Paranoid psycho novels from the late 1970's and early 1980's (The Face That Must Die)
3. Shift to meaty atmospheric stuff in the 1980's and 1990's (Midnight Sun, and initial black humor horror things like The Count of Eleven)
4. Decisive shift to darkly satiric paranoid horror in the 2000's (The Grin in the Dark, Thieving Fear)
5. A return to the Lovecraftian approach in the 2010's, but utilizing techniques developed in the prior decades (The Last Revelation of the Gla'aki; Creatures of the Pool)

I personally am the biggest fan of periods 2 and 5, with the remaining three in honorable second place. To me, the biggest draw of Mr. Campbell is his use of language, which, when at its best, is elegant, sophisticated, and poetically luminous.