Complex sentence: His talents in other directions of art were of a very ordinary kind, but as an interpreter and illustrator of Dickens's characters, "Phiz", as he always signed his drawings, was exceptional, surpassing his rivals Cruikshank and Leech.
Split into simpler sentences: His talents in other directions of art were of a very ordinary kind. But as an interpreter and illustrator of Dickens's characters, "Phiz", as he always signed his drawings, was exceptional, surpassing his rivals Cruikshank and Leech.