Thanks to Triablogue of this long summary from New Testament scholar Craig Keener:
“Readers throughout most of history understood the Gospels as biographies (Stanton 1989a: 15-17), but after 1915 scholars tried to find some other classification for them, mainly because these scholars compared ancient and modern biography and noticed that the Gospels differed from the latter (Talbert 1977: 2-3; cf. Mack 1988: 16n.6). The current trend, however, is again to recognize the Gospels as ancient biographies. The most complete statement of the question to date comes from a Cambridge monograph by Richard A. Burridge. After carefully defining the criteria for evaluating genre (1992: 109-27) and establishing the characteristic features of Greco-Roman ‘lives’ (128-90), he demonstrates how the canonical Gospels fit this genre (191-239). The trend to regard the Gospels as ancient biography is currently strong enough for British Matthew scholar Graham Stanton to characterize the skepticism of Bultmann and others about the biographical character of the Gospels as ‘surprisingly inaccurate’ (1993: 63; idem 1995: 137)….But though such [ancient] historians did not always write the way we write history today, they were clearly concerned to write history as well as their resources allowed (Jos. Ant. 20.156-57’ Arist. Poetics 9.2-3, 1451b; Diod. Sic. 21.17.1; Dion. Hal. 1.1.2-4; 1.2.1; 1.4.2; cf. Mosley 1965). Although the historical accuracy of biographers varied from one biographer to another, biographers intended biographies to be essentially historical works (see Aune 1988: 125; Witherington 1994:339; cf. Polyb. 8.8)….There apparently were bad historians and biographers who made up stories, but they became objects of criticism for violating accepted standards (cf. Lucian History 12, 24-25)….Matthew and Luke, whose fidelity we can test against some of their sources, rank high among ancient works….
Like most Greek-speaking Jewish biographers, Matthew is more interested in interpreting tradition than in creating it….A Gospel writer like Luke was among the most accurate of ancient historians, if we may judge from his use of Mark (see Marshall 1978; idem 1991) and his historiography in Acts (cf., e.g., Sherwin-White 1978; Gill and Gempf 1994). Luke clearly had both written (Lk 1:1) and oral (1:2) sources available, and his literary patron Theophilus already knew much of this Christian tradition (1:4), which would exclude Luke’s widespread invention of new material. Luke undoubtedly researched this material (1:3) during his (on my view) probable sojourn with Paul in Palestine (Acts 21:17; 27:1; on the ‘we-narratives,’ cf., e.g., Maddox 1982: 7). Although Luke writes more in the Greco-Roman historiographic tradition than Matthew does, Matthew’s normally relatively conservative use of Mark likewise suggests a high degree of historical trustworthiness behind his accounts….only historical works, not novels, had historical prologues like that of Luke [Luke 1:1-4] (Aune 1987: 124)…A central character’s ‘great deeds’ generally comprise the bulk of an ancient biographical narrative, and the Gospels fit this prediction (Burridge 1992: 208). In other words, biographies were about someone in particular. Aside from the 42.5 percent of Matthew’s verbs that appear directly in Jesus’ teaching, Jesus himself is the subject of 17.2 percent of Matthew’s verbs; the disciples, 8.8 percent; those to whom Jesus ministers, 4.4 percent; and the religious establishment, 4.4 percent. Even in his absence he often remains the subject of others’ discussions (14:1-2; 26:3-5). Thus, as was common in ancient biographies (and no other genre), at least half of Matthew’s verbs involve the central figure’s ‘words and deeds’ (Burridge 1992: 196-97, 202). The entire point of using this genre is that it focuses on Jesus himself, not simply on early Christian experience (Burridge 1992: 256-58).” Craig Keener -A Commentary On The Gospel Of Matthew [Grand Rapids, Michigan: William B. Eerdmans Publishing Company, 1999], pp. 17-18, 21-23, 51)