Robert M. Grant , A Historical Introduction to the New Testament, , Chapter 10: The Gospel of Luke and the Book of Acts
Although the end was postponed, as Matthew envisioned, we should not agree that it was originally regarded as imminent. Similarly while Luke minimizes Jewish-gentile differences it is possible that in Galatians Paul exaggerates them. The fact that Acts reflects certain purposes on its author's part does not mean that views contrary to those purposes are necessarily authentic, or more authentic.
Richard Heard , An Introduction to the New Testament, , Chapter12: The Study of the Acts of the Apostles; Acts is our most important historical source for the earliest development of Christianity, and as such of immediate relevance for present-day Christians.