Full Idea
Deriving many Tarski-biconditionals is not a sufficient condition for being a good theory of truth. A good theory of truth must in addition do justice to the compositional nature of truth.
Clarification
'Compositional' means assembling complex things from simple components
Gist of Idea
A good theory of truth must be compositional (as well as deriving biconditionals)
Source
Leon Horsten (The Tarskian Turn [2011], 06.1)
Book Reference
Horsten,Leon: 'The Tarskian Turn' [MIT 2011], p.70