While most evangelicals have never heard of Louis Gaussen, his Theopneustia lurked in the backdrop of evangelical discussions of inspiration for the better part of a century. (For the argument for this, see Kenneth J Stewart's "A Bombshell of a Book: Gaussen's Theopneustia and its Influence on Subsequent Evangelical Theology, Evangelical Quarterly July 2003). In many ways, Gaussen framed the evangelical position, and consequently evangelical attempts to rehabilitate that position.
Gaussen's work emphasizes the divine aspect of Scripture, to the extent that Gaussen had to write a follow up work (Le Canon des saintes écritures au double point de vue de la science et de la foi) arguing that he does not subscribe to a mechanical theory of inspiration. Gaussen argues forcefully that all of Scripture--the thoughts and the very words themselves are inspired.
Along the way, he emphasizes his disdain for the burdgeoning liberal German theological tradition of which Schleiremacher (who argues for the primacy of religious experience) is representative. He also rejects the notion that there are degrees or types of inspiration, arguing that such distinctions are a priori and non-Biblical.
Additionally, he is adament in his position that inspiration is about the text, not the authors. He dismisses inquiry into the mechanics of inspiration as interesting, but not material to the question of inspiration. Gaussen argues that communication in texts are similar to communication between persons: just as souls need bodies to transmit information, so meaning needs words. Questioning the inspiration of the words themselves undercuts the possibility of revelation itself, which, of course, is what the Bible is all about.
The emphasis on the inspiration of the words, however, poses problems for Gaussen. He is forced to do backflips to resolve the Bible and science, a problem that still lurks for many evangelicals.
Additionally, he is forced into the position that all genres of Scripture are "prophecy," as it is prophecy in which God speaks in, through, and for man. Such a reduction of biblical types is interesting, but ultimately seems rather difficult to defend.
Gaussen's work is important for more than just its historical influence. While the scientific arguments are probably outdated, Theopneustia is a stirring work of devotional theology. Gaussen is passionate in his reverence of Holy Scripture, and even those who disagree with his conclusions can't help but be moved by his pleas to honor God in His Word.