Sinclair Ferguson's introduction (available online for free) is a helpful overview of the New Perspective, filled with a number of helpful point. Here's one:
It has been implied and sometimes stated by adherents of the New Perspective that the Reformers were mistaken in virtually equating the Judaizers who plagued the church with the “salvation without grace” teaching they saw in late medieval church life. But this seriously misconstrues if not misrepresents the historical situation.
In fact the late medieval church was almost obsessed with grace – and how the individual gets “more” of it by doing what he can. The Reformers well understood that Roman Catholic theology did not outright deny the necessity of grace. Rather they recognized that the “grace” referred to was really not grace at all – since its reception was so conditioned on a man’s good works. To
say “grace” is by no means the same thing as to understand or teach “grace.” One should never be misled by the regular occurrence of the word “grace” into assuming that a biblical understanding of grace is well understood.
The result of this – paradoxically – is that at times one has the impression that the New Perspective fails to notice a strikingly similar phenomenon in Second Temple Judaism, or glosses over it when it appears: the use of the language of “grace,” when in context the “grace” in view is conditioned on man. It is in fact compromised grace, not true grace. It turns out, after all, that while the pattern of the Old Testament’s teaching is that fellowship with God is by pure grace, that grace is at times greatly dis-graced in the rabbinical literature, as it frequently was in the history of the covenant people. Even the notion that the reason Yahweh is so gracious to his poor people is because they have suffered so much turns out to be grace compromised by its conditionalism: there is a reason to be found in man to “explain” why, or to whom, God is gracious. But true grace cannot thus be qualifi ed without being distorted.
With regard to N.T. Wright, Ferguson comments in a footnote:
In an illuminating personal note Bishop Wright comments on the “vital and liberating point” which he first met in the work of the sixteenth-century Anglican theologian Richard Hooker, that one is not justified by faith by believing in justification by faith (What Saint Paul Really Said, London, 1997, p.159). What strikes one as curious about this statement is that while such a discovery would indeed be liberating, one would be hard pressed to find an intelligent evangelical in the history of the church who has taught such a distorted view of the gospel.
You can listen to a lecture by Ferguson on the NPP
here.