I have discussed the overwhelming exegetical problems with the Reformed understanding of the verb λογιζομαι and texts that allegedly teach imputed righteousness (e.g., Gen 15:6; Gen 31:15;Lev 17:3-4/Deut 25:1, etc.)
For a very good scholarly refutation of John Piper’s arguments in favour of imputation, see the following article:
Don Garlington, Imputation or Union with Christ? A Response to John Piper
Garlington does a stellar job at showing how Piper’s Reformed theology cannot stand up to the light of sound exegesis, providing further proof that Reformed theology is a blasphemous legal fiction that makes God a liar.
As an aside, to see further evidence of Piper’s incompetence with the biblical texts, see N.T. Wright, Justification: God's Plan & Paul's Vision (IVP Academic, 2009).