One of the main reasons why many of Wright’s critics misunderstand his doctrine of justification can be traced to the fact that the questions that he is answering with his doctrine of justification are slightly different from those which traditional Reformed doctrines of justification are designed to answer.
Reformed doctrines of justification tend to have an anthropological starting point. The big question that the doctrine generally addresses is that of how an individual can get right with a holy God. Wright’s doctrine, on the other hand, takes its starting point with God. He starts with God’s covenant-renewing action in the gospel, rather than with man’s attempt to get right with God. Justification is understood in the context of the question of how God sets men to rights, rather than primarily in the context of the question of how men can get right with God.
When Wright talks about the basis for God’s justifying declaration, he is not providing a direct answer to the question of what we must do to be saved. For Wright, God’s declaration that we are right with Him is not merely delivered on the basis of Christ’s perfect righteousness extra nos, but includes the work of the Spirit within the believer as part of its basis. Wright believes that God is righteous in justifying because (a) Christ has died for the sins of the world; (b) faith is the appropriate helpless response to the gospel; (c) faith is the true obedience that the Law called for but could never provide; (d) faith, as the first sign of the work of the Spirit, is the sign of a new life that is obedient by nature (‘God’s verdict in the present is righteous, because the basis on which it is made is sufficient grounds for confidence that it will correspond to the righteous verdict of the last day’).
Wright’s doctrine of justification relies heavily on the work of the Holy Spirit in the convert (both in present and final justification). If Wright’s doctrine were designed as a direct answer to the traditional Reformed questions of justification it would probably be dangerously misleading. We would be taught to depend at least in part on the work of the Spirit in ourselves, an incomplete and imperfect righteousness within, rather than on the completed work and person of Christ extra nos. Such a dependence on an incomplete righteousness would produce assurance problems, given the lack of a proper ground for our justification (the need for a perfect righteousness as the basis of our justification is the issue that the doctrine of the imputation of Christ’s righteousness seeks to deal with). However, Wright’s doctrine is not designed as an answer to the traditional questions that Reformed Christians have tended to use the doctrine of justification to answer. To understand Wright’s doctrine of justification you really have to put the traditional questions to one side, something which most of Wright’s critics haven’t really grasped yet.
When Wright speaks of faith in relation to his doctrine of justification one of the things that should really strike the reader is how passive man is characterized as being. From his treatments of faith in such contexts, one could be led to wonder whether he believes that faith is something that human beings ‘exercise’ at all. For instance, faith is spoken of as the ‘boundary marker’ or ‘badge’ of the true people of God. One does not generally think in terms of ‘exercising’ a badge.
‘Faith’, for Paul, is therefore not a substitute ‘work’ in a moralistic sense. It is not something one does in order to gain admittance into the covenant people. It is the badge that proclaims that one is already a member. [What St Paul Really Said, 132]
Such a statement is bound to confuse the Reformed reader who is used to approaching the doctrine of justification as the doctrine that answers the question of what an individual must do to get right with a holy God. Given Wright’s theological — rather than anthropological — starting point, his doctrine of justification provides at best a confusing answer to the question that Reformed Christians are answering.
As Wright addresses the issue of justification within the context of the question of how God sets humanity and His creation to rights, his doctrine can include things that a doctrine with an anthropological starting point would find it hard to include. If we adopt an anthropological starting point, certain of the distinctions between justification and sanctification are far more important than they are if we begin with a theological starting point. From an anthropological starting point justification speaks of the way in which I can come to be accepted as righteous in God’s sight and sanctification speaks of a more synergistic process, through which I grow in personal righteousness. Viewed from this perspective it is crucial to keep justification and sanctification distinct, as we do not want to say that we are accepted as righteous in God’s sight on the basis of our works. The distinction between justification and sanctification is essential if we are to preserve monergism.
Viewed from Wright’s more theological starting point, justification and what we call sanctification are not so distinct. From a theological starting point sanctification is not really viewed as an essentially synergistic process (although from other perspectives it can legitimately be regarded as such). In Wright’s understanding, God’s declaration of justification has ‘sanctification’ — both present and promised — in view to some extent. However — and this point is absolutely crucial — the sanctification that is in view is God’s action, rather than ours. It is God who gives the badge of faith and the life of the Spirit in the effectual call and it is God who commits Himself to bringing to completion that which He has begun in us. The condition for this justification is something provided by God, rather than by us.
This means that Wright can maintain a far less antithetical relationship between faith and faithfulness in his doctrine of justification. He writes:
Faith and obedience are not antithetical. They belong exactly together. Indeed, very often the word ‘faith’ itself could properly be translated as ‘faithfulness’, which makes the point just as well. Nor, of course, does this then compromise the gospel or justification, smuggling in ‘works’ by a back door. That would only be the case if the realignment I have been arguing for throughout were not grasped. Faith, even in this active sense, is never and in no way a qualification, provided from the human side, either for getting into God’s family or for staying there once in. It is the God-given badge of membership, neither more not less. [What St Paul Really Said, 160]
All of this should alert the reader to the fact that Wright is not approaching justification as the answer to the question of what one must do to be saved. If someone asked Wright what they must do to be saved, he would clearly direct them to Jesus Christ and away from any dependence upon their own moral efforts. He would call them to trust in God, His Word and His promises, and not to rest their assurance on their own imperfect works. There is no ambiguity on this point. However, this is not the question that Wright believes that the doctrine of justification is intended to answer. Few points could be more important for the proper interpretation of Wright.
Almost three years ago now, 
N.T. Wright replies to someone involved in translating Judas and the Gospel of Jesus, who wrote to him, troubled by some of the libellous claims about Wright and his beliefs that he encountered online:

The first half of the paper will be primarily methodical; the second half primarily exegetical. We currently face a puzzle of perception. There are those in the Church who are troubled by what they see as the hardening of theology into dry doctrine. Scripture, they believe, brings life, not ‘doctrine’. Scripture can often function like a favourite movie or symphony for them. For others, however, Scripture has become as dry as doctrine itself. Extended prayer and praise meetings are what they regard as important — the Spirit. In addition to such people there are those who love dogmatic theology and are bored by labyrinthine exegesis.