I'm great playing Scott Joplin music (7)
I believe the answer is:
ragtime
'scott joplin music' is the definition.
(I've seen this before)
'i'm great playing' is the wordplay.
'playing' indicates an anagram.
'im'+'great'='imgreat'
'imgreat' with letters rearranged gives 'RAGTIME'.
(Other definitions for ragtime that I've seen before include "Early jazz style" , "Form of jazz with a two-four rhythm" , "Migrate to find jazz music" , "Kind of jazz for Maigret" , "Syncopated music genre" .)